Talk:Paper - On the postnatal development of the ovary (albino rat), with especial reference to the number of ova (1920)
On The Postnatal Development Of The Ovary (Albino Rat), With Especial Reference To The Number Of Ova
Hayato Arai
The Wistar Institute of Anatomy
FOUR CHARTS
INTRODUCTION
Numerous data on the postnatal development of the ovaries of lower mammals are to be found, but, so far as I am aware, there are no investigations on the number of ova in these animals. For the human ovaries, however, there are five observations on the number of ova, though the techniques used by several authors are open to some criticism.
Strange to say, despite the great emphasis recently placed on the study of reproductive phenomena, especially in relation to the questions of inheritance, sex difference, or of physiology of the internal secretions, no one has attempted to obtain fundamental data on the number of ova in the ovaries, although such data may throw some definite light on the various problems in the physiology of reproduction.
I have taken this study of the total number of ova in the rat during the entire span of life at the suggestion of Prof. H. H. Donaldson, to whom I am happy to acknowledge my indebtedness not only for his deep interest shown during the progress of the work, but also for numerous suggestions while preparing this paper.
I shall first present the data on the number of ova in human ovaries as reported by the five investigators.
Henle ('73) estimated the number of the follicles in an ovary of an eighteen-year-old woman, and stated that it contained about 36,000 follicles, or not less than 72,000 in both ovaries. The method by which he estimated this number is as follows:
405
406 • HAYATO AEAI
Ich ziihltc in einem Sagittalschnitte aus dem Ovarium eines 18 jahrigen ^liidchens, welcher etwa den scchsten Theil der Peripheric umfasst, 20 solcher Blaschen; langs der ganzen Peripherie des Frontalschnittes wiirden deren also etwa 120, langs der Peripherie eines, dem langsten Diirchmesser des Ovarium parallelen Durchschnitts vielleicht 300 anzunehmen sein, und sonach wiirde die Zahl der Blaschen in einem Ovarium etwa 36,000, in beiden nicht viel weniger als 72,000 betragen
Thus Henle counted the number of the follicles contained in one-sixth of one section and then obtained his result by multiplying this number of ova by the total number of sections.
Heyse ('97) counted more exactly the number of follicles in the ovary of a woman seventeen years old. The method which he adopted was as follows:
Ich zahlte in jedem der 42 Schnitte die Follikel und maass unterm Mikroskop die Flachenausdehnung jedes einzelnen Schnittes aus. Die Summe aller Follikel betrug 1165, die von der Summe der Schnitte eingenommene Flache umfasste 1996 qmm. Da die Dicke der einzelnen Schnitte 0.05 mm. betrug so ergiebt sich ein Rauminhalt von 100 cbmm. auf welchen also die Zahl von 1165 Follikeln kommt. Nach Angaben von Gegenbaur und Vierordt nahm ich den Inhalt des gazen Ovariums zu 3600 cbmm. an, danach wiirden im ganzen Ovarium ziemlich 42,000 Follikel zu zahlen sein. Indessen besteht noch eine Hauptfehlerquelle. Wenn von den durchgezahlten Schnitten zwei unmittelbar auf einander gehoren, so werden die einzelnen, durchschnittenen Follikel in jedem der beiden Schnitte gezahlt werden, also doppelt; Graafsche Follikel wiirden so sogar vielfach in Rechnung gesetzt werden. Aber audi wenn die einzelnen Schnitte durch dazwischen liegende Substanz getrennt sind, werden immer dem einzelnen Schnitte eine Anzahl Follikel zugerechnet, die mit ihrem Haupttheile ihm gar nicht angehoren. Daher werden also alle Follikel, die nicht auf einen Schnitte beschrankt sind, implicite doppelt gezahlt. So habe ich daher an 10 meiner Schnitte noch festgestellt, wieviel von den iiberhaupt in ihnen zahlbaren Follikeln mit ihrem Centrum, oder bei den grosseren mit der Eizelle, in den Schnitten lagen. Ich fand, dass diese 41.95 procent der Gesammtmenge betrugen. Von den oben erhaltenen 42,000 Follikeln nahm ich daher auch 41.95 procent und es ergab sich als wirkliche Anzahl, der in dem normalen Ovarium vorhandenen Follikel (abgerundet) 17,600.
By the method just stated, Heyse determined the number of follicles in both ovaries to be 35,200. Heyse also obtained his number by estimation.
This method of Heyse is certainly more exact that Henle's, but it is not sufficiently so because, according to Vierordt's table
NUMBER OF OVA! ALBINO RAT 407
('06), the thickness of the ovary of a woman nineteen years old is on the average (left and right) 13.4 mm. If the sections were made 0.05 mm. in thickness, the total number of sections would be at least 270. From 270 sections, therefore, Heyse selected only forty-two sections, that is about one-sixth of the total ovary. Moreover, the distribution of follicles in the mature ovary is not so uniform as in the ovarj^ of the new-born, but varies enormously between two sections when taken some distance apart. Therefore, Heyse should have counted at least half of the total ovary in order to obtain a fairly approximate number,
Joessel and Waldeyer ('99, p. 793) state that both ovaries of a new-born child contain 100,000 or more ova, but it is explicitly added that this is merely an estimate and probably too low rather than too high.
Sappey ('79) made a determination of the number of ova by counting those found in 1 sq. mm. of the section and then computing the number which should be present in the entire ovary. His numbers are very large. In one girl of three years he estimated 422,000 ova in one ovary. In another of four years 675,000, and in a third child 300,000. In a young woman of eighteen years he reports 300,000 in one ovary. Why these numbers are so high I cannot at the moment say.
The latest study on the number of ova in man is that by v. Hansemann ('13). I have taken the liberty of tabulating his results, which were obtained by counting the number of ova in every fifth section from a complete series of sections for each ovary. The number of ova thus counted was multiplied by five, and the results are those given. It is difficult to determine from the text whether the final number represents the ova in one or in both ovaries, but I assume that the numbers are for one ovary only.i
^ Several of the authors here quoted on the number of ova in man do not make it plain whether their numbers apply to one ovary or to both, so that I have had to decide the question by inference in most cases. In the article by v. Hansemann ('13) reference is made to the statement by Minot ('92) that there are 70,000 ova in man. This is evidently based on Henle's determination. Waldeyer ('06) (in Hertwig's Handbuch) states that there are probably 50,000 ova in each ovary of the human fetus.
408 HAYATO ARAT
Number of ova in one (?) ovary of man at different ages (v. Hansemann)
Age ■ Number of Ova
6.5 months 30,339
1 year 2 months 48,808
2 years 46, 174
8 years 25,665
10 years 20,862
14 years 16,390
17 to 18 years 5,000-7,000
While there is still some doubt whether the numbers given by V. Hansemann are for one or for both ovaries, yet they show clearly what the previous data suggest; namely, that there are many more ova present during the earliest years of life than at puberty, and that even after puberty the numbers show a significant decrease.
To obtain some accurate information regarding the relation between the number of ova and the age of the animal, I have utilized the ovaries of albino rats.
MATERIAL AND TECHNIQUE
The material used in this study was all supplied from the rat colony at The Wistar Institute. The number of rats examined for the standard table was thirty-nine — from one day after birth to 947 days of age — and the material was collected during seven months — from April to November, 1918.
In each instance the body weight, body length, the weights of the ovaries, and the appearance of corpora lutea were recorded. The removal of the ovary, especially when the rats are very small, requires some practice. Each ovary was quickly weighed and then fixed in Bouin's solution for from six to eight hours. The material was washed in running water for twenty to thirty minutes, sometimes for one hour, run through the alcohols, cleared in xylol, and finally imbedded in paraffin. Each entire ovary was sectioned in series at 10 n, and the sections were stained with hematoxylin and eosin.
In order to obtain approximately the true number of ova in the ovaries, I have counted under the microscope the nucleus of every ovum in the series of sections obtained from each entire
NUMBER OF OVA! ALBINO RAT 409
ovary. The nuclei which were counted were those most distinctly stained by hematoxylin. The diameter of the nuclei of the ova range from 8 to 12 /x both in the primitive ova and in the definitive ova. By this method we might make a double counting occasionally, because it is based on the counting of the distinctly stained nuclei. On the other hand, there is no fear of missing ova, because the sections were 10 /x thick, while the smallest nucleus has a diameter of 8 At at least.
For counting the number of ova in younger ovaries, especially those before twenty days of age, the use of the net-micrometer is necessary. For the measurement of the diameter of the larger ova a Zeiss compens. ocular no. 6 and object. 4 was used and the micrometer eyepiece was so adjusted that each division equalled 4 /x. I have divided all the ova, according to their diameters, into four groups:
Group Diameter
I less than 20^l
II 20 to 40m
III 40 to 60m
IV over 60m
We find ova, especially in the mature ovaries, which show several stages of degeneration. These stages I have divided into four groups.
A. The follicles are poorly developed and have one to three layers of cells. In the centrum the ovum is not found, but instead there is a homogeneous hyalin mass which stains red with eosin.
B. The follicles which belong to this group show merely the outline of the ova in follicles, but the ovum is without a nucleus. Such ova stain red with eosin but faintly.
C. In this group the follicles are well developed, and sometimes are almost like the mature follicles, having many layers of follicle cells, but these cells are either already degenerated or are about to degenerate. In these follicles the large cavity usually contains fluid or sometimes a colloidal mass which stains a deep red with eosin. However, no ova can be found. The shape of the follicles is either circular or oval.
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, NO. 4
410 HAYATO ARAI
h D. In this group the follicles show an appearance similar to those in Group C, but the outline of the ova shows an irregular contour and the nucleus cannot be found. Sometimes we find numerous cell contours, devoid of nuclei, which are stained more plainly by eosin than normal ova. Whether these numerous cell contours were produced from many ova or from degenerated follicle cells which have fallen into the cavity, is not yet determined.
In the ovary after about sixty to seventy days of age corpora lutea are present. These we divided into two groups according to their characters, while each of these may be further subdivided into two subgroups.
A. Large corpora lutea. 1. The corpus luteum which belongs to this subgroup is large in size and its lutein cells show no degenerative processes. It contains some blood in its centrum, and the lutein cells are full size.
2. Those belonging to the subgroup (2) show the lutein cells less fresh, and signs of degeneration are present. Whether or not these two subgroups of large corpora lutea are produced as the result of pregnancy, is not clear.
B. Small corpora lutea. In this second group the corpora lutea are' small and the lutein cells in process of degeneration. Among them we can distinguish two forms: B (1) in which the corpus luteum is rich in blood capillaries and its lutein cells are fresh in appearance while in
B (2) the lutein cells appear to be resorbed and in their place the connective tissue appears, but this form can hardly be distinguished from the so-called 'corpora lutea atresia.'
We have counted separately the entire number of normal ova, making four groups according to diameter, the degenerate ova and the corpora lutea in each ovary — right and left side — and finally the total number of ova has been obtained by adding the numbers of ova found in both ovaries.
NUMBER OF OVA: ALBINO RAT 411
OBSERVATIONS
Under this head we shall merely present and describe our results, leaving the interpretation of them for the section entitled 'Discussion.' "
1. The comparison between the weight of ovaries and number of ova
on the right and left sides
There is, so far as I am aware, no statement concerning either the weight relations of the right and left ovaries, or concerning the number of ova in these.
To determine the weight relation between the ovaries when the left ovary is taken as the standard, we divide the entire series into two groups according to the presence or absence of the corpora lutea.
A. This group contains all cases in which the weight of one ovary is less than 10 mgm. and no corpora lutea are present. There are twenty such cases (up to 110 days), eleven of these have the ratio smaller than one, and seven the ratio larger than one, while in two cases the ratio equals one. The average ratio of all twenty cases is 0.93 for the right ovary. This ratio seems to indicate that in the absence of the corpora lutea the right, ovary tends to be lighter than the left, though the difference is not great.
B. To this group belong all cases in which the weight of one ovary is greater than 10 mgm. and which show corpora lutea. We have altogether sixteen cases, among these thirteen cases show the ratio smaller than one, while three show the ratio more than one. The average of the ratios of the entire sixteen cases is 0.85 for the right ovary, thus giving a greater difference between the right and left ovaries in this group than in the former. The ratios for all thirty-six cases become 0.90, thus revealing clearly a tendency at all ages for the right ovary to weigh less than the left.
On the relative weights of the right and left ovaries of other mammals there are no observations. Wiedersheim ('97) states that in birds the right ovary undergoes an early and more or
412 HAYATO AIL\I
less complete atrophy. In passing we may note that Riddle's ('18) observations on the testes of pigeons and doves show that in healthy birds the right testis is larger than the left in most cases, so that in bu^ds asymmetry of the gonads appears in both sexes, but in opposite senses.
Since, as we shall see, the weight of the ovaries is influenced mainly by the abundance of well-developed folHcles and of corpora lutea, it appears to me probable that the larger ovary should be better developed in this respect than the smaller.
The numbers of ova found in the two ovaries show the following ratios (table 1). The numbers of ova found in the right ovary were compared with those found in the left, taking the left as the standard. Out of the thirty-nine cases, seventeen show the ratios smaller than one; two show their ratios as 1.00, while in the remaining twenty cases the ratios are larger than one.
The averaged ratios in the two lots range from 0.91 to 1.12 for the right ovary. The average of all the thirty-nine cases gives the ratio of 1.03 for the right ovary, thus showing that the difference in the number of ova in the two ovaries is very slight.
From the above it is clear that the right ovary contains approximately the same number of ova as the left or a few more, despite the fact that it weighs somewhat less.
The apparent contradiction thus revealed may be due to the presence in the left ovary of a greater number of the larve ova, as well as of certain stages of the degenerating follicle, and may be influenced also by a slight inequality of the corpora lutea on the two sides.
If with these suggestions in mind we consult table 1, it appears that the combined numbers for the various classes of larger ova (more than 20 ix in diameter) are approximately the same in both ovaries, and by consequence the numbers of the smaller-sized ova are also approximately equal. It has not been deemed necessary to put in the numbers for the ova under 20 ix in diameter, as these may be obtained by subtraction. From the fact that while the total number of ova contained in both the right and the left ovary is approximately the same, while nevertheless the
TABLE 1
Giving with ages the number of ova in the left and the right ovary — together with their respective weights. Also the relative weights of the right ovary and the relative number of ova in it. The numbers for the corpora lutea are also given.
LEFT OVARY
RIGHT OVARY
RATIOS
AGE
Weight
of ovary
left
Ova
Corpora lutea
Total
Weight
of ovary right
Ova
Corpora lutea
Total
Number
of ova
right to
left
Weight of ovary
Over 20 m
Total
Over 20 /u
Total
right to left
days
7ngm.
nigm.
1
16,807
18,298
1.09
3
174
14,138
208
14,114
1.00
5
462
11,829
516
13,757
1.17
7
1.1
500
10,850
0.7
475
10,135
0.93
0.64
10
1.2
291
7,735
1.0
289
7,671
0.99
0.83
15
1.3
411
8,246
1.1
382
7,630
0.93
0,85
20
3.0
492
5,329
3.4
494
5,747
1.08
1.13
26
6.2
404
5,501
4.6
355
4,921
0.89
0.74
30
3.1
341
6,109
3.6
260
6,432
1.05
1.16
36
3.0
152
4,344
2.6
186
4,705
1.09
0.87
36
5.2
200
4,654
5.2
233
4,344
0.94
1.00
41
4.2
162
5,523
3.2
138
6,448
1.17
0.76
41
7.4
238
5,446
6.6
203
4,827
0.89
0.90
46
8.1
193
4,605
6.0
138
5,761
1.25
0.75
50
5.6
192
5,478
5.6
143
5,555
1.01
1.00
50
5.9
201
5,059
7.0
183
5,014
0.99
I.IS
60
5.6
141
5,192
4.7
139
5,260
1.01
0.84
64
4.9
183
4,917
3.0
179
5,114
1.04
0.61
64
15.1
327
4,623
6
16.0
307
5,450
8
1.18
1.06
70
26.5
181
3,569
18
17.3
179
3,037
13
0.86
0.65
80
4.4
139
4,335
5.0
169
4,231
0.97
1.14
80*
19.0
184
2,305
20
18.4
330
2,963
19
1.28
0.97
84
12.2
160
4,736
8
10.0
154
4,984
5
1.05
0.82
95
5.4
245
4,959
6.8
226
5,805
1.17
1.26
95*
50.0
179
3,406
24
23.5
169
3,208
22
0.94
0.47
100
4.7
123
3,400
4.1
86
2,341
0.69
0.94
100
6.4
96
3,449
6.7
119
3,619
1.05
1.05
110
9.8
140
2,964
9.9
152
2,429
0.82
1.01
110
21.6
229
3,724
31
20.0
225
4,020
29
1.08
0.92
140
26.4
228
4,549
15
22.8
190
4,528
14
1.00
0.86
' 150
18.9
183
4,528
16
13.6
219
4,495
23
0.99
0.72
198
27.3
'158
1,491
32
30.8
124
1,259
31
0.89
1.13
206*
29.3
137
4,090
32
25.5
147
3,976
24
0.97
0.87
262
26.1
107
1,626
42
22.8
104
2,121
50
1.30
0.87
318
21.9
128
2,960
45
14.6
114
2,742
24
0.93
0.67
385
38.0
176
2,339
19
44.6
157
2,163
30
0.93
1.16
454
19.3
131
2,264
48
14.5
163
2,495
45
1.10
0.75
559*
38.4
79
2,181
17
35.1
85
2,812
21
1.29
0.91
947
34.1
106
999
56
31.1
104
920
52
1.03
0.91
AveraE
es bef(
Dre appearance
of corp
ora lut(
3a. . . .
1.03
0.88
Avera^
5es afte
r appearance o
F corpo
ra lutes
L
1.03
0.91
Pregnant.
413
414
HAYATO ARAI
right ovary is smaller, it seems reasonable to infer that the right ovary may be slightly retarded, and consequently is smaller and also contains more ova than the left, as the number of ova decreases with increasing age.
This conclusion seems to be supported by the fact that previous to the first appearance of the corpora lutea at sixty-four days
40000
35000
30000
25000
20000
15000
10000
5000
Number of ova (total'
1 1 1
_J_
•
«
i_ t
t- it
^^H
' I ,
- ; ^5 V 4^
., X V- ^ 4^
■tii' \ ^
-^ \ 7-'-^-
_ _ _^_ ^^ ___ = --__^___ ___
^ + _
O 100 200 300 400 500 600 700 800 900 tOOO
Age— days
Chart 1 Showing the total number of ova in both ovaries of the albino rat at different ages (in detail).
the average relative weight of the right ovary is 0.88, while after this age it is 0.91 (bottom of table 1).
071 the 7iumber of ova in relation to age
In table 2 the data on the thirty-nine rats are given.
As will be seen from both table 2 and chart 1, the total number of ova counted in both ovaries one day after birth was 35,105. This number decreases rapidly to 11,000 at twenty days, after which there is a very slow decrease to about 10,000 at sixty-four
NUMBER OF OVA I ALBINO RAT
415
TABLE 2 The relation between the age and the total number of ova, and of corpora lutea
X
o ^
n
a §
Si
o J
n
WEIGHT OF BOTH OVARIES
NUMBER OF OVA
NUMBER OF CORPORA
LUTEA
AGE
Less than 20 M
20 to 40
40 to 60
More than 60 m
Total
Small
Large
Total
days
grams
mm.
mgm.
1
5.5
47
35,105
35,105
3
7.3
52
27,870
382
28,252
5
10.6
60
24,608
978
25,586
7
13.9
69
1.8
20,009
974
2
20,985
10
14.8
76
2.2
14,826
542
38
15,406
15
20.5
83
2.4
15,083
470
323
15,976
20
23.7
89
6.4
10,090
404
469
113
11,076
26
30.2
95
10.8
9,663
322
275
162
10,422
30
34.8
108
6.7
11,940
279
208
114
12,541
36
34.9
105
5.6
8,711
152
124
62
9,049
36
50.0
122
10.4
8,565
184
137
112
8,998
41
58.2
131
7.4
11,671
204
59
37
11,971
41
61.9
128
14.0
9,832
229
121
91
10,273
46
69.5
142
14.0
9,935
156
115
60
10,266
50
74.6
146
11.2
10,698
197
74
64
11,033
50
75.5
144
12.9
9,689
236
98
50
10,073
60
93.5
145
10.3
10,173
149
91
40
10,452
64
62.7
132
7.9
9,669
189
106
66
10,030
■ 64
113.5
165
31.1
9,439
398
187
47
10,073
6
8
14
70
106.3
162
42.8
6,246
197
99
64
6,606
9
22
31
80
77.3
140
9.4
8,258
189
77
42
8,566
80*
107.3
153
37.4
4,564
290
179
145
5,268
26
13
39
84
125.0
165
22.2
9,406
177
85
52
9,720
2
11
13
95
98.5
148
12.2
10,293
276
109
86
10,764
95*
160.0
182
73.5
6,266
129
109
110
6,614
33
13
46
100
97.8
156
13.1
6,853
133
43
39
7,068
16
7
23
100
78.5
138
8.8
5,535
110
75
24
5,744
110
94.3
147
18.7
5,100
176
75
41
5,392
110
167.1
185
41.6
7,290
307
101
46
7,744
40
20
60
140
123.0
168
49.2
8,659
243
113
62
9,077
12
17
29
150^
129.5
171
32.5
8,621
222
138
42
9,023
18
21
39
198
142.7
171
58.1
2,468
164
100
18
2,750
33
30
63
206*
188.5
185
54.8
7,782
155
97
32
8,066
33
23
56
262
145.0
182
48.9
3,536
126
70
15
3,747
61
31
92
318
155.0
189
36.5
5,460
126
87
29
5,702
53
16
69
385
161.3
194
82.6
4,169
222
93
18
4,502
24
25
49
454
138.7
194
33.8
4,465
160
78
56
4,759
67
26
93
559*
198.7
200
73.5
4,729
107
37
20
4,893
27
11
38
947
238.0
215
65.2
1,709
128
61
21
1,919
90
18
108
Pregnant.
416
HAYATO ARAI
days. At this age the corpora lutea may appear, that is at about sixty-four days ovulation occurs. From sixty-four days on the total number of ova decreases slowly but steadily to about 2,000 at 947 days. This was the oldest rat available for study. Using the ratio of the span of life, 1 to 30, which we commonly employ when comparing the rat with man, 947 days for the rat is equivalent to seventy-eight years for man.
va
of
arge
r
sizes
600
500
A
^
400
B C
_
40-60"
300
ou
"
200
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Age-days
Chart 2 Showing the total number of ova, as well as the number of ova of different sizes in the albino rat at different ages (condensed).
On account of the high individual variation, I have averaged the data in table 2 and given the averages in table 3 and chart 2 with the hope that the data thus arranged might reveal more clearly the real tendency to the changes in the number of ova according to the age of the rat.
From birth up to 110 days the number of ova in the ovaries of the rats were grouped together within ten-day intervals, and after 110 days at intervals of about fifty days. The results of this grouping are shown in table 3 and chart 2. We notice that from the averages of four to twenty-three days the mean total number decreases very rapidly, from 27,483 to 10,746 ova, and
NUMBER OF OVA! ALBINO RAT
417
from twenty-three to sixty-three days the number of ova with sHght variations diminishes from 10,746 (twenty-three days) to 10,185 (sixty-three days). From sixty-three days on it decreases rapidly at first, then rather steadily to 559 days, dropping markedly at the last entry for 947 days.
TABLE 3
The relation between the age and the number of ova in both ovaries; the average numbers. This is the fundamental table used for the discussion
NUMBER OF
NUMBER OF OVA
CORPORA
NUM
INTERVAL OF . AGE
AGE
BOOT WEIGHT
BODY LENGTH
WEIGHT OF BOTH OVARIES
LUTEA
BER
OF
RATS
C
is
1^
a.
o
o ^^ o
5.
o o
a
I-. o
"3
O
"3
a
03
"3 o
days
daijs
grams
mm.
mgm,.
4
1-7
4
9.3
56
26,898
584
1
27,483
2
10-15
12
17.7
80
2.3
14,954
506
181
15,641
2
20-26
23
26.9
92
8.6
9,877
362
372
138
10,746
3
30-36
34
32.6
112
7.6
9,737
205
156
96
10,196
3
41-46
43
63.2
134
11.8
10,479
196
98
63
10,836
2
50-50
50
75.0
145
12.1
10,193
217
86
57
10,553
3
60-64
63
89.7
147
16.4
9,760
245
129
51
10,185
2
3
5
1
70
106.3
162
43.8
6,246
197
99
64
6,606
9
22
31
3
SO-84
81
103.2
153
23.0
7,439
217
114
80
7,850
9
8
17
4
95-100
97
108.4
156
28.6
7,237
162
84
65
7,548
12
9
21
2
110-110
110
130.7
166
30.1
6,195
241
88
44
6,568
20
10
30
3
140-198
163
131.7
170
47.1
6,583
209
117
41
6,950
21
23
44
2
206-262
234
166.7
184
51.9
5,659
141
83
24
5,909
47
27
74
2
318-385
351
158.4
192
59.2
4,814
174
90
24
5,102
38
21
59
1
454
138.7
194
33.8
4,465
160
78
56
4,759
67
26
93
1
559
198.9
200
73.5
4,729
107
37
20
4,893
27
11
38
1
947
238.0
215
65.2
1,709
128
61
21
1,919
90
18
108
Chart 2 shows two sharp drops; the first drop extends from four to twenty-three days and the second extends from sixty-three to seventy days, with a period of relative constancy between twentythree and sixty-three days. The significance of these phases will be taken up later (p. 440).
Since the total number of ova includes ova of various sizes, I have attempted to analyze the general graph — chart 2 — into its
418 HAYATO AIL\I
components in order to throw some light on the growth of the several groups.
The graph for the number of ova with diameters less than 20 /jl would be nearly the same as that shown by the graph for the total number of ova, and has therefore not been drawn.
The form of the graph for the number of ova with diameters of 20 to 40 ^<, however, shows a slight difference. The number decreases rapidly from four days until twenty-three days, and then continues to decrease gradually till 947 days, the fluctuations in number being apparently due to individual variation.
The graph for the number of ova with diameters of 40 to 60 /jl increases rapidly from twelve days and reaches its maximum at twenty-three days. After twenty-three days it decreases again at first rapidly, then more gradually.
The graph for the number of ova with diameters more than 60 )U shows a rapid decrease from twenty-three days to fortythree days. After forty-three days it shows but a very slight fall. It is to be noted that as the diameters of the ova increase, the age of their appearance advances.
We can obtain more clearly the relative growth of these groups of ova from table 4, in which the total number of ova is taken as the standard, and the numbers of ova of various sizes are represented as the percentages of this total. The percentage values of the number of ova with diameters less than 20 ix range from 100 per cent to 88 per cent of the total throughout the entire span of life. Within these two limits there are numerous fluctuations, the reasons for which will be discussed later.
Taking the entire series from twenty days, when the largest follicles appear, to 559 days, the approximate age of the menopause, the average percentage values for the several classes of ova are —
Under 20 /x = 95.0 per cent 20 to 40 A( = 2.7 per cent 40 to 60 /i = 1.5 per cent Over 60 /x = 0.8 per cent
1. Immediately after birth both the absolute number of small ova, as well as their percentage values, decrease rapidly, reaching
NUMBER OF OVA: ALBINO RAT
419
TABLE 4 Percentage values of the member of the ova of various sizes to the total number of ova
AGE
MEAN NUMBER
OF OVA PER MILLIGRAM OF OVARY WEIGHT
THE PERCENTAGE VALUES OF GROUPS OF OVA
Less than 20 n
20. to 40 n
40 to 60 n
More than 60 yu
days
per cent
per cent
per cent
per cent
1
100.0
3
98.7
1.3
5
96.2
3.8
7
1,166
•95.4
4.6
0.0
10
700
96.2
3.5
0.3
15
661
95.0
3.0
2.0
20
173
91.1
3.7
4.2
1.0
26
97
92.7
3.1
2.6
1.4
30
189
95.2
2.2
1.7
0.9
36
161
96.3
1.7
1.4
0.7
36
86
95.2
2.1
1.5
1.3
41
161
97.5
1.7
0.5
0.3
41
73
95.7
2.2
1.2
0.9
46
73
96.8
1.5
1.1
0.6
50
98
97.0
1.8
0.7
0.6
50
77
96.2
2.3
1.0
0.5
60
101
97.3
1.4
0.9
0.4
64
127
96.4
1.9
1.1
0.6
64>
32
93.7
4.0
1.9
0.5
701
15
94.6
3.0
1.5
1.0
802
14
88.3
5.5
3.4
2.8
80
91
96.4
2.2
0.9
0.5
841
44
96.8
1.8
0.9
0.5
952
9
94.7
2.0
1.6
1.7
95
88
95.6
2.6
1.0
0.8
100
54
97.0
1.9
0.6
0.6
100
65
96.4
1.9
1.3
0.4
100
29
94.6
3.3
1.4
0.8
1101
17
94.1
4.0
1.3
0.6
1401
18
95.4
2.7
1.2
0.7
1501
28
95.5
2.5
1.5
0.5
1981
5
89.7
6.0
3.6
0.7
2062
15
96.5
1.9
1.2
0.4
2621
8
94.4
3.3
1.9
0.4
3181
15
95.8
2.2
1.5
0.5
3851
5
■ 92.6
4.9.
2.1
0.4
4541
14
93.8
3.4
1.6
1.1
559*
7
96.7
2.2
0.8
0.4
9471
3
89.1
6.7
3.2
1.1
' Corpora lutea present. - Pregnant.
420 HAYATO ARAI
a minimum at about twenty days. This striking phenomena is associated with the rapid increase of the larger ova during this period. From twenty days up to about thirty-six days, the percentage value increases again, though the absolute number of the small ova is decreased, owing to the appearance of the larger ova (table 2). From thirtj^-six to sixty-four days the percentage values for the number of small ova are approximately constant. This is associated with slight numerical changes in the number of ova of all sizes.
2. Between 64 and 110 days, in those ovaries in which corpora lutea have not yet appeared, the percentage values of the small ova range from 94.6 per cent to 97 per cent. In the ovaries in which the corpora lutea have appeared, but excluding the pregnant animals, the number of small ova ranges from 93.7 per cent to 96.8 per cent, showing no change in the number of these cells in relation to the appearance of the corpora lutea.
3. From 140 to 947 days the corpora lutea are always present and the percentage values fluctuate about a mean value of 94 per cent, the very oldest rat giving 89 per cent. Therefore, generally speaking, the percentage values of the small ova (less than 20 fji diameters) remain constant in the older rats.
4. In the pregnant rats — four cases — we find the percentage values 95 to 97 per cent in three cases and 88 per cent in one, which is the youngest. For this unusual value we have no explanation.
From the foregoing it seems that the percentage values for the ova under 20 fx decrease rapidly from one day after birth till twenty days. This is followed by an increase of 4 per cent up to thirty-six days. From thirty-six days on to the end of the series the percentage values remain nearly constant (the four pregnant cases are not included in this general statement).
The number of ova 20 to 40 ^^ in diameter show percentage values which increase rapidly from three days up to seven days, at which age they reach a maximum of 4.6 per cent. This initial increase is followed by lower values up to sixty-four days, after which there is a slight tendency to higher percentages with advancing age.
NUMBER OF OVA: ALBINO RAT 421
The percentage values for the number of ova with diameters from 40 to 60 n increase rapidly from ten days to twenty days, at which age they reach an absolute maximum. This in turn is followed by a rapid decrease till forty-one days.
From forty-one days on to 947 days the percentage values remain less than 2 per cent, except in three cases. There seems to be, however, a slight tendency for the percentage values in this group to increase in the older animals.
The ova more than 60 ix in diameter only once represent more than 2 per cent of the total and usually less than 1 per cent, so that no attempt is made to correlate the variations in their abundance with other changes.
In this table are the determinations for four pregnant rats. In the ovaries from a rat pregnant at eighty days the percentage values of all ova with diameters more than 20 n are considerably higher than in the ovaries of non-pregnant rats, but in the remaining three cases this peculiarity does not appear. Whether this is a significant difference cannot at the moment be determined.
From table 4 it may be seen that in the ovaries in which corpora lutea are absent the mean number of ova per 0.1 mgm. of ovary weight tends to run inversely to the percentage value for the number of ova having a diameter of 60 fj. or more, and a similar relation holds after the corpora lutea appear in the ovaries. It therefore follows that in the former cases the number of largest ova is in large measure responsible for the greater weight of ovary, while in the latter cases both the largest ova and the corpora lutea may be taken as the responsible factors.
It should be stated that in young ovaries there are also many larger ova with diameters 40 to 60 ix or more, though it is questionable whether these are mature because the layer of follicle cells is about three to four cells thick, and moreover the cavity is not yet formed. I am rather inclined to believe that these ova are in the first stage of degeneration rather than in a stage of development. After thirty days we find in the ovaries many well-developed follicles, which not only have a cavity, but many layers of follicle cells, and as in the mature follicles the cumulus
422
HAYATO ARAI
ovigerus is well developed. These follicles contain ripe ova, whose diameter is usually 60 to 66 ju. Sometimes we observe a very large ovum with a diameter of 76 jj. or more, but such an ovum may be in an early stage of degeneration, because both the nucleus and cell body are not well stained, as in the case in the normally ripened ovum.
The numbers of the mature follicles and of largest ova in both ovaries are given in table 5.
As is shown in table 5, the number of the mature follicles is not strictly proportional to the number of the largest ova with
TABLE 5 The numbers of mature follicles and of largest ova in both ovaries
AGE
NUMBER OF
MATURE FOLLICLES
NUMBER OF LARGEST OVA
AGE
NUMBER OF
MATURE
FOLLICLES
NUMBER OF LARGEST OVA
days
daps
46
15
60
1401
22
62
64
3i
66
150'
26
42
641
39
47
1981
16
18
802
38
145
206"
12
32
80
23
42
262"
15
15
100
21
39
318"
18
29
100
16
24
385'^
9
IS
110
23
41
559?
13
20
110'
25
46
9471
19
21
1 Shows presence of corpora lutea.
2 Stands for pregnancy.
a diameter of 60 fx and more. Nevertheless, if we consider the data from forty-six to one hundred days the number of largest ova are a little more than twice as numerous as the mature follicles, while in the remainder of the table they are a little less than twice. Thus there is a, tendency for the proportion of largest ova to slightly diminish with age.
We notice also that in the rat from sixtj^-four to eighty days the number of mature follicles ranges from thirty-one to thirty-nine, and this large number of follicles may be related to the attainment of sexual maturity, since after eighty days the number of follicles tends to decrease. The mean number of these mature follicles in all eighteen cases is twenty-one.
NUMBER OF OVA: ALBINO RAT 423
3. On the number of ova in relation to body weight
The data on the number of ova have been arranged according to the increasing body weight and the results are shown in table 6 and chart 3. In order to eliminate the individual fluctuations as much as possible, I have averaged the data which belong to the rats whose body weights difl'er not more than 10 grams from one another. From this table the pregnant rats have been omitted, because the weight of the foetuses was not recorded and consequently the true bod}^ weight of these pregnant rats cannot be accurately estimated. When these average values are plotted, we obtain the graph shown in chart 3.
It is evident from table 6 and chart 3 that the total number of ova decreases rapidly from 5.5 grams — one day after birth — until about 33 grams, and then after remaining at about the same value till 64 grams, decreases again gradually up to 238 grams.
The corpora lutea appeared first in the ovary of a rat with a body weight of 102 grams, and all rats which 'possessed a body weight heavier than 102 grams invariably showed corpora lutea. The general form of the graph shown in chart 2 is as a whole similar to that shown in chart 3.
The graph showing the number of ova with diameters less than 20 fi is approximately similar to the graph which shows the variation of the total number, but the latter graph only has been drawn. The graph showing the number of ova in the three groups having diameters 20 to 40 ^u, 40 to 60 fx, and over 60 ijl are quite similar to the corresponding graphs based on age (chart 2) and do not call for special comments.
The number of the large corpora lutea is nearly the same 15 to 14 at 102 to 122 grams, but increases to a maximum (29), and then after 142 grams falls off slightly. Similarly, the number of smaller corpora is at first nearly constant, but increases markedly toward the end of the series (chart 3).
When we compare these graphs for the number of ova according to body weight (chart 3) with those according to age (chart 2), we find a slight difference in their form. At twenty-three days we find in table 3 a body weight of 26.9 grams and at sixty
424
HAYATO AIL\I
three days, 89.7 grams. If, now, chart 3 is examined, we see that between these body-weight limits the number of ova shows httle change — just as it did between the corresponding age Umits in chart 2. The fall in number after the body weight of 89.7 grams is, however, less marked in chart 3 than after sixty-three days in chart 2. This slight difference is due to the fact that
1000 900 800 700 600
500 400 300 200
too
35000 30000 25000 20000 15000 10000 5000
Ova of large
sizes
'
1?5
Number of corpora lutea
1
-\
rota
J
^
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20-f u
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40-60 f
k
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Number of ova itotali
1
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50
100
150
200 2 50
Body weight-gms.
Chart 3 Graph showing the relation between the body weight and the total number of ova in both ovaries, together with the number of the corpora lutea and of the three groups of ova more than 20m in diameter.
some of the older rats were ill nourished and small for their age. This is shown by table 7, in which the observed body weights for given ages are compared with the expected ages as recorded by Donaldson ('15).
As these figures show, the coincidence between the two series of ages is fair except for the last two body-weight groups. The animals in these groups were light for their age.
NUMBER OF OVA I ALBINO RAT
425
4. On the number of ova and the body length
I have arranged the number of ova according to the body length of the rats, and the results are given in table 8. Graphs
TABLE 6
The relation between the body weights and total number of ova in both ovaries; average number. From this table the pregnant rats ivere omitted
NUMBER OF
NUMBER OF
OVA
CORPOR.'^ LUTEA
WEIGHT
NUM
OF
BER
INTERV.\L OF
BODY
BOTH
a.
a.
^
OF
BODY WEIGHT
WEIGHT
o3
K
5^.
RATS
HIES
C
o=i
5^9
"5
3
S
03
1-4
Rats without corpora lutea
1 1 1
2 2
3 2
3 4 3
grams
grams
5.5
7.3
10.6
mgm.
35,105 27,870 24,608
382
978
35,105 28,252
25,586
13.9-14.8
14.3
2.0
17,417
758
20
18,195
20.5-23.7
22.1
4.4
12,587
437
396
56
13,476
30.2-34.9
33.3
7.7
10,105
251
202
113
10,671
50.0-58.2
54.1
8.9
10,118
194
98
75
10,485
61.9-69.5
64.7
11.9
9,812
191
114
72
10,189
74.8-78.3
76.5
10.6
8,545
183
81
45
8,854
93.5-98.5
95.4
13.8
8,522
167
92
56
8,837
Rats with
corpora lutea
2
97.8-106.3
102.0
32.0
6,549
165
71
52
6.837
12
15
27
4
113.5-129.5
122. S
33.8
9,031
260
131
51
9,473
10
14
24
3
138.7-145.0
142.1
46.9
3,490
150
83
30
3,753
54
29
83
3
155.0-167.1
161.1
53.6
5,640
218
94
31
5,983
39
20
59
1
238.0
65.2
1,709
128
61
21
1,919
90
IS
108
have been made for these data also, but they show relations which in all respects are so similar to those obtained when the data are plotted on body weight that they are now omitted. It is to be noted that when rats reach a body length of 148 mm. ovulation occurs almost invariably, as shown in tables 2 and 8, and I shall take up this point in the discussion.
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, NO. 4
426
HAYATO ARAI
TABLE 7 Data on body weight according to age
bodt weight of rats
(averaged in grams)
(observed)
THE AGE OP R-'i.TS (.VVERAGED
IN days) (observed)
THE STANDARD AGE IN DAYS CORRESPONDING TO BODY WEIGHT (DONALDSON, '15)
5.5 22.0 33.0 64.0 95 102
1
18 31 50
88
85
1
21 32 53
68 72
TABLE 8
The relation between the body length and the number of ova in both ovaries; average
numbers
1 1 1
2 2 2 2 3 5 3
NUMBER OF
NUMBER OF
OVA
CORPORA LUTEA
NUMBER
INTERVAL OF
BODY
OF BOTH
C
a.
o
3.
o
OF
BODY
LENGTH
OVA
S
RATS
LENGTH
RIES
■^ a.
M^
T a.
^^
^
a
„_
o
o
SS
a o
03
s
CS
c3 O
cs
■^
s
H
M
tJ
H
Rats without corpora lutea
mm.
mm.
47 52 60
mgm.
35,105
27,870 24,608
382 978
35,105
28,252 25,586
69-76
73
2.0
17,417
758
20
18,195
83-89
86
4.4
12,587
437
396
56
13,476
95-105
100
8.2
9,187
237
200
112
9,736
108-122
115
8.6
10,252
232
173
113
10,770
128-132
130
9.4
10,391
207
95
65
10,758
138-145
142
11.1
8,718
168
91
43
9,020
146-148
147
14.1
8,697
216
86
64
9,063
Rats wi
th corpora lutea
2
153-156
155
28.7
5,754
211
111
92
6,168
21
10
31
4
162-168
168
36.6
8,438
254
121
56
8,809
7
15
22
2
171-171
171
45.3
5,544
193
119
30
5,886
26
25
51
4
182-185
184
54.7
6,218
179
94
51
6,542
42
22
64
4
189-200
194
56.6
4,706
. 154
74
31
4,965
43
20
63
1
215
65.2
1,709
128
61
21
1,919
90
18
108
NUMBER OF OVA: ALBINO RAT 427
If we compare the body lengths of the rats here employed with those for the standard values given by Donaldson ('06), we obtain the following relations (table 9) .
This shows the larger rats to be short for their age — a relation which would naturally follow from those found in table 7 for the body weights.
5. On the number of ova and the weight of the ovaries
The numbers of ova have been arranged according to the observed weight of both ovaries, in order to examine the relationship between these two characters (table 10). For convenience the data on the weights of the ovaries were divided into two
TABLE 9 Relations of body length on age
BODY LENGTH AVERAGED
AVEBAGE AGE
STANDARD AGE CORRESPONDING TO THE BODY LENGTH
mm.
47 100
147
days
1
31
85
days
29 61
groups: a) the ovaries without corpora lutea and, h) the ovaries with corpora lutea.
We find rather high individual variations in this relation, as indicated in table 2. However, table 10 shows that when the weight of the ovaries reaches from 1.8 to 2.2 mgm., the ova 40 to 60 n in diameter are present, and in the ovaries of 2.4 to 5.6 mgm. the ova with aid ameter of more than 60 {j. are found. It is again to be noted that the first corpora lutea are seen in ovaries which weigh 20 mgm., and therefore in the ovaries which weigh more than 20 mgm., the relation between the number of ova and the weight of ovaries becomes highly complex, owing to the appearance of corpora lutea, the number and size of which are the most important factors in modifying the weight of the ovaries.
We notice from chart 4 — based on table 10 — that the number of ova falls steadily up to an ovary weight of 6.5 mgm. This is
428
HAYATO ARAI
followed by a period of approximate constancy up to an ovary weight of 16.5 mgm., the end of the period preceding the appearance of the corpora lutea. This stage, marked by a break in the graph, passes into the stage in which the corpora lutea appear, and after the appearance of the corpora lutea the graph
1000 900 800 700 600 500 400 300 200
too
35000
30000
25000
20000
15000
10000
5000
Ova o( larger
Sizes
,
1
r
-
fl
-
'>C\-A.{\ u
I
B
-
40-60 "
._C
-over 60"
^!_
1
I
i
t
p
__
1
.1
1
s
^
■■
J \
^
K^
r
^^ A
1 T
A.
M
_
J
,
—
—
L
,^
l^X."
>
-«
^ "
^
•
■«■
-
—
( —
..
_
_
L , .
p
•tzV
<
VI,
- >
?'
V
—
-■*
■A
_
0^
-ir--'
"
>- —
""■-^ iC
otaO
Number of ova u
^
^
I J
Tit
M
4-^
1
1^4 -A
,
^
•
>--i
1
N
'^
^<
■«.
»
A
—J
,
.
,_
10 20 30 40 50 60 70 80
Weight of ovanes in milligrams
Chart 4 Graph showing the relation between the weight of both ovaries and the total number of ova, together with those of the three groups more than 20 m in diameter. The graphs are broken after puberty.
for the total number of ova falls very slowly to the end of the record. The several graphs for the number of ova more than 20 IX in diameter are very similar in form to the corresponding graphs in chart 3 and are subject to a like interpretation.
It may be appropriate, however, to call attention here to the relations of the various groups of larger ova. In the first place, all the larger ova are derived from small ova. Moreover, the
NUMBER OF OVA! ALBINO RAT
429
arrangement in groups is for convenience merely, and they represent in reality a continuous series. It follows from this that the groups of smallest diameter should be the first to appear and
TABLE 10 The relation between the weight of both ovaries and the number of ova; average number
NUM
INTERVAL
OF OVARY
WEIGHT
WEIGHT OF BOTH OVAHIES
BODY
WEIGHT
NUMBER OF OVA
NUMBER OF CORPORA LUTEA
BER
OP
RATS
is hi
a.
o o o
3.
§
o o
c
e2
"3
S
03 1^
3
o Eh
Rats without corpora lutea
1 1 1 2 2 2 3 3 3 2 2
mgm.
mgm. 0.61
grams
5.5
35,105
35,105
1.01
7.3
27,870
382
28,252
3.31
10.6
24,608
978
25,586
l.S-2.2
2.0
14.3
17,417
756
20
18,195
2.4-5.6
4.0
27.4
11,897
311
224
31
12,463
6.4-6.7
6.5
29.2
11,015
341
189
114
11,659
7.4-8.8
8.0
66.5
8,958
168
80
42
9,248
9.4-10.4
10.0
73.6
8,999
174
102
65
9,340
10.8-12.2
11.5
67.8
10,216
265
153
104
10,740
12.9-14.0
13.5
68.7
9,760
233
110
70
10,173
14.0-18.9
16.5
81.9
7,517
166
95
51
7,829
Rats with corpora lutea
2
20 . 1-22 . 2
21.2
111.4
8,129
155
64
46
8,394
9
9
18
3
31.1-33.8
32.5
127.2
7,508
260
135
48
7,951
31
23
54
3
36.5-41.6
38.5
143.1
5,802
241
122
73
6,238
40
16
56
3
43.8-49.2
47.3
124.8
6,147
189
94
47
6,477
27
23
50
2
54.8-58.1
56.4
165.6
5,125
159
99
25
5,408
33
27
60
2
65.2-73.5
69.4
199.0
3,987
129
85
66
4,267
61
16
77
2
73.5-82.6
78.0
180.1
4,449
164
65
19
4,697
26
18
44
1 Ovary weights were taken from 'The Rat' for the observed body weights.
the other groups follow, in time of appearance, in the order of their size.
Table 10 and chart 4 show that this is what occurs. Further, at the time of first appearance any group is represented by only a small number and the appearance of the next group coincides with the maximum number in the group just preceding. The
430 HAYATO ARAI
group with the smallest diameter (20 to 40 /x) is most subject to degeneration, for the numbers in it fall most rapidl}' and continuously. The group with the largest diameter (more than 60 //) is most constant in number. This relation does not necessarily mean that these largest ova persist for any long period, but merely that the balance between their formation and degeneration is rather evenly maintained.
The first phase of the graph for the entire number of ova may be interpreted as due to the fact that during this phase many primitive germ cells are growing rapidly, yet at the same time an excess of cells is undergoing degeneration, so that the number falls rapidl}^
From 8 up to 16.5 mgm. in ovary weight the enlargement of newly formed definitive ova is mainly responsible for the increase in the weight of the ovaries, containing a nearly constant number of ova. All the groups of ova more than 20 fx in diameter behave in much the same manner. After such ova are first recognized there is a short period in which they increase in number, followed in each group by a more or less pronounced decrease to the end of the series. On the whole, then, the total number of ova decreases according as the ovaries grow in weight, and in the first phase this decrease is very rapid, but from a weight of 6.5 mgm. it becomes much slower.
The number of ova less than 20 ^c in diameter is not plotted on this chart, but, as table 10 shows, it would give a curve practically identical with that for the total number.
The comparison of my own data on the weights of the ovaries with those given by Donaldson ('15) shows the following relations according to age (table 11).
So far as the critical periods for the data are concerned, there is good agreement beween the two determinations in table 11, but the last entry indicates that my animals were somewhat retarded. The data show that the weights of the ovaries hold an inverse relation to the number of ova, that is, the heavier the ovaries the fewer are the ova in them. This inverse relation may be due in part to the formation of the interstitial tissue, but depends mainly on several other factors, such as the corpora lutea, the number of well-developed follicles, degenerate follicles, etc.
NUMBER OF OVA: ALBINO RAT
431
DISCUSSION
The various topics will be discussed in the order in which the data have just been presented.
1 . Comparison of the weights of the ovaries and the number of ova
on the right and left sides
The data in table 1 show that the right ovary has, as a rule, only nine-tenths the weight of the left, but nevertheless contains the same (or a slightly greater) number of ova.
TABLE 11 The weights of both ovaries with ages
THE AGE CORRESPONDING TO
THE AGE CORRESPONDING TO
THE WEIGHT OF BOTH
THESE AVERAGE
THESE AVERAGE
OVARIES
OVARY WEIGHTS IN DAYS
OVARY WEIGHTS IN DAYS
(my OBSERVATION)
(DONALDSON, '15)
mgm.
6.5
25
26
10.0
59
55
11.5
57
57
21.2
92
67
It is interesting to note further that, so far as my observations go, the corpora lutea appear simultaneously in both ovaries when these reach the weight of more than 10 mgm. (for one ovary). They are not present earlier (table 1), and in no case do they appear on one side only. Sobotta ('10) found that, as a rule, in albino rats the mature ova are discharged at the same time from both ovaries.
We might expect this relation in other mammals which normally produce two or more young at a birth, but we have not found any observations on this point.
It is usually stated that in man only one ripe ovum at a time is discharged from either of the ovaries, and therefore in man the corpus luteum should appear on one side only. Whether the left or right human ovary supplies most of the ova or whether both ovaries give off the same number is not known. One striking relation worth emphasizing here is that variations in the
432 HAYATO ARAI
numbers of ova tend to be similar in both ovaries, even in the cases where the total number is markedly low (see 198 day rat in table 1 as the extreme instance), Approximate equality is also found for the numbers of ova on the right and left sides if the means of the values for the low records at 80, 100, 110, 198, and 262 days are compared. These are: right ovary 2223 and left ovary 2357.
The growth of ovary in weight according to age
The growth of the ovary of the albino rat after birth has been studied by Jackson ('13) and Hatai ('13, '14), and it shows several phases. Jackson, who constructed a chart showing the relative weight of ovaries on body weight, pointed out two of these; the first phase beginning at birth showing an increase to a maximum at a body weight of 10 to 15 grams, followed by a decrease up to a body weight of 60 grams. At 60 grams a second period of acceleration, which corresponds to the advent of puberty, begins, and during this phase the ovaries increase to a second maximum at 110 to 120 grams in body weight. After this the relative weight steadily decreases. To make a comparison with Jackson's results I have prepared table 12.
This shows that according to my data the relative weight of ovaries increases to the first maximum at a body weight of 22 to 33 grams, and then decreases gradually until a body weight of 95 grams. After 95 grams the curve rises rapidly at 102 grams in body weight. About this time corpora lutea appear in the ovaries, and the maximum relative weight is reached at a body weight of 142 to 161 grams, after which it decreases. In general the two sets of observations agree.
The disagreement in the exact periods of the maxima between Jackson's data and my own may be caused by the smaller number of rats (thirty-nine) used by me. The explanation as to the true significance of the two maxima is difficult, especially the first maximum, owing to the complexity of the factors which enter into the growth of ovaries, such as the enlargement of follicles, the increase of stroma tissue, etc. The cause for the second maximum may be interpreted as follows :
NUMBER OF OVA! ALBINO RAT
433
According to Donaldson ('15), the corresponding ages for the body weight of 110 to 120 grams in the female albino rat is about seventy-five to eighty days, and as ovulation has occurred at this age fresh corpora lutea are already present. According to Jackson, ovulation, that is the age of puberty, takes place at seventy
TABLE 12 The relation between the body weight and the weight of both ovaries; average number
NUMBER OF RATS
INTERVAL OF BODY WEIGHT
BODY WEIGHT
OBSERVED
WEIGHT OF
BOTH
OVARIES
WEIGHT OP
BOTH OVARIES
IN
MILLIGRAMS ACCORDING TO BODY WEIGHT (DONALDSON)
PERCENTAGE
WEIGHTS
OF OVARIES ON
BODY WEIGHT
OBSERVED
Rats
without corpora lutea
grams
days
grams
7ngm.
1
1
5.5
1.1
1
3
7.3
2.0
1
5
10.6
3.4
2
13.9-14.8
9
14.3
2.0
4.3
0.014
2
20.5-23.7
18
22.1
4.4
5.8
0.020
3
30.2-34.9
31
33.3
7.7
7.2
0.023
2
50.0-58.2
39
54.1
8.9
8.9
0.016
3
61.0-69.5
50
64.7
11.9
9.4
0.018
4
74.8-77.3
70
76.5
10.6
13.2
0.014
3
93.5-98.5
88
95.4
13.8
24.7
0.014
Rat
^ with corpora lutea
2
97.8-106.3
85
102.0
32.0
31.4
0.031
4
113.5-129.5
110
122.8
33.8
43.9
0.027
3
138.7-145.0
305
142.1
46.9
46.2
0.033
3
155.0-167.1
271
161.1
53.6
47.4
0.033
1
947
238.0
65.2
50.0
0.027
From thi.s table the pregnant rats were omitted.
days. In my rats, however, the age of seventy days is represented by a rapid increase in the weight of the ovaries, but they have not j^et attained their maximum. Consequently the second maximum of Jackson, or the period of rapid increase, would be caused principally by the formation of a number of corpora lutea in the ovaries.
434 HAYATO ARAI
We have seen that in general the weight of ovaries in which the corpora lutea are not present increases with the growth of the rat, either in body weight or body length. With the appearance of the corpora lutea the weight of the ovaries becomes more fluctuating, owing perhaps to individual variations in the addition of the corpora lutea.
Thus these fluctuations just noted may have no meaning except as showing a greater variation in the growth rate of the ovary at this period. Even when the weights of the ovaries found by myself and those given by Donaldson are arranged according to the increasing body length, the results show a high degree of similarity to those which were arranged according to increasing body weight (table 11). My observations show that with the appearance of corpora lutea there is a sudden increase in the weight of the ovaries, and we may infer, therefore, that the increase in the weight of ovaries with increasing body weight, as noted in 'The Rat,' chart 21, is also due to the same cause.
In woman the ovaries are said to atrophy after the menopause, so the weight of ovaries might show a decrease after this event. Such weight alterations, as well as the period at which the maximum weight is attained, are not recorded in the literature. It would therefore be of interest to extend these observations to human ovaries.
We may now summarize the various factors which are responsible for the increase in the weight of the ovaries. In addition to the formation and enlargement of the individual ova, these are the growth of interstitial tissue, the number of the mature follicles; of degenerated follicles, small or large; of corpora lutea, fresh or old, as well as the content of blood. The exact amount of blood, however, has not been determined, yet it is worth while to note here that either a hyperaemic or anaemic state is recognizable according to the different physiological states of the ovary in relation to heat.
NUMBER OF OVA: ALBINO R-\T 435
On the number of ova in relation to age
As was stated earlier, the total number of ova is greatest during the first days after birth, some ovaries containing as many as 35,105 ova. This number, however, decreases rapidly with increase of the ovaries in weight until it drops to about 11,000 at twenty days. From twenty-three days to sixty-three days the total number of ova varies only slightly — that is, from about 11,000 to 10,000. At about sixty-three days ovulation appears. The number of ova then decreases at first rapidly from about 10,000 at sixty-three days to about 2,000 at 947 days. The variation in the total number of ova according to increasing ages is different from that in most other organs of the rat, as, for instance, in the brain, in which the number of cells not only increases during the earlier period of growth, but soon becomes nearly constant, the individual neurons persisting for the most part throughout the entire span of life.
The progressive changes in the form of the graph (chart 2) at the different periods seem to be related to several factors, such as the new formation of ova, their degeneration, etc., and I wish to discuss these factors now.
The new formation and the degeneration of ova
According to Kingery's observation on the white mouse ('17), the proliferation of cells from the germinal epithelium does not take the form of tubular down-growth, but the cells are grouped in irregular masses just beneath the epithelium. The cell masses are made up of oocytes and indifferent cells or future follicle cells. In the course of development some of the flattened adjacent epithelial cells completely surround the oocyte which is still in the germinal epithelium. As growth proceeds, the other cells of the germinal epithelium extend up over this oocyte in its primary follicle, .which is in this manner left behind in the tunica albuginea under the epithelium, and thus gradually passes through the tunica to reach the stroma beneath.
Since my study was concerned principally with the ova number and not with questions of the oogenesis, I am not prepared
436 HAYATO ARAl
to discuss Kingery's statement concerning the proliferation of the germ cells from the germinal epithelium in foetal life. However, in the ovaries of albino rats after birth the manner of the proliferation of germ cells appears to be similar to that described by Kingery. In my case the oocytes from the germinal epithelium begin to form at about ten to fifteen days after birth. The nuclei are large relatively to the cell body, nearly filling the cell, which begins to grow and enlarge in situ in the germinal epithelium. The shape of these cells is at first more or less spherical, and they are larger than the other epithelial cells. As they enlarge, the adjacent epithelial cells are crowded to either side, and when the development of the egg cells proceeds further, they are enclosed by the flattened epithelial cells, thus forming the primary follicle.
At this time the layer of tunica albuginea appears to be single or double, but as the development proceeds the follicles pass through the tunica albuginea into the stroma. This new formation continues with the growth of the ovaries, and the number of the follicles thus formed may reach its maximum at the period of puberty.
After puberty this process of new formation may yet continue, but is not as active as before puberty. Within the first ten days after birth this proliferation of new egg cells cannot usually be seen.
According to Kingery, in the mouse the cavity in the larger follicles begins to appear between fifteen and eighteen days after birth and a degeneration of the egg cells sets in at about the same time. In the albino rat the cavity in the large-sized follicles begins to appear at about twenty-days after birth, and at about twenty-six days the middle-sized degenerating follicles, according to my classification, are to be seen.
Kingery stated that the formation of egg cells from epithelium is most rapid from three to twenty-five days after birth and that it goes on practically up to sexual maturity, although more slowly in the later part of this period. It is completed at forty or fortyfive days after birth, at which age, as a rule, female mice are sexually mature.
NUMBER OF OVA I ALBINO IL\T 437
My own observations on the rat naturally show some slight difference in the age periods from those given by Kingery. In the rat the first appearance of the newly formed follicles is at about ten days after birth, and their number increases until about sixty to seventy days, at which age as a rule ovulation occurs; but this process continues at least to the age of one year, though not as rapidly as before.
The problem as to the origin of the definitive ova is not yet definitely settled. Some authors, Jenkinson ('13), Kirkham ('16), d'Hollander ('04), and Sonnenbrodt ('08), stated that the definitive ova are formed from the primordial germ cells, though some observers, Dustin, Karchakewitsch, Allen and Skrobansky (cited from Oogenesis in the white mouse," '17), Winiwarter and Sainmont ('08), consider that the primordial germ cells mainly degenerate, and thus, as the rule, the definitive ova cannot be produced from these. Kingery holds the opinion that the definitive ova are developed from the primary follicles formed after birth, but he did not state clearly the relation between the primordial germ cells of other authors and the definitive ova of his own designation.
There is not much literature on the new formation of the egg cells after birth. Van Beneden ('80) described in the adult bat the egg cells as formed from the germinal epithelium. LaneClaypon ('05), in the ovary of the rabbit, concluded that the follicle cells and the interstitial cells are formed from the germinal epithelium. These interstitial cells, from their origin, are potential egg cells, and under the proper stimulus, are capable of developing into ova. Von Winiwarter and Sainmont ('08) stated that in the cat, at about the age of three and one-half to four months, a renewal of the activity (the third proliferation) of the germinal epithelium produces a new supply of germ cells which develop into the definitive ova, when all the egg cells of the first (embryonic) and second (shortly after birth) proliferations have degenerated; and he stated further ('08) that these definitive ova come either entirely from the third proliferation or partly from it and partly from the undifferentiated cells left over from the second proliferation.
438 HAYATO ARAI
Kingsbury ('13) inclines to the opinion that there is no evidence of a new formation of ova by the third proUferation of Winiwarter and Sainmont. Van der Stricht ('11) does not discuss at all the new formation of ova, but simply states that in the adult ovary in cats the definitive ova are derived from the second proliferation. Felix ('12), in describing the development of the ovary in man, states that after the tunica albuginea is formed, in embryos of 180 mm. in length, no egg cells can be added to the interior of the ovary from the epithelial layer, and thus, according to this author, there is no possibility of a new formation of ova from the germinal epithelium.
Kingery ('17), in his studies on the white mouse, states that there is a new formation of germ cells after birth, and that the definitive ova come from the primary follicles. Briefly put, Kingery believes that at birth all the cells of the germinal epithelium seem equally capable of developing into oocytes, follicle cells or epithelial cells, though it is not evident just what factors are responsible for their eventual fate. As the ovary becomes more mature and the cells better differentiated, this potentiality of the cells of the germinal epithelium is lost, and after sexual maturity no more egg cells or follicle cells are derived from the epithelium.
He states also that all the egg cells of the first or embryonic proliferation in the mouse undergo degeneration and disappear. In ovaries of mice, from about seventeen days after birth up to sexual maturity, and at the adult stage, egg cells in their follicles may be seen in various stages of degeneration and atresia.
This is the evidence, of course, that a large number of these germ cells of embryonic origin degenerate and are resorbed. The degeneration of the definitive ova, which in all likelihood sets in before sexual maturity, is continued through the whole sexual life of the individual, as is well known. Since, then, a large number of definitive ova degenerate, and since these are situated more superficially than the primitive germ cells, which are mostly degenerated, it seems reasonable to conclude that all the primitive germ cells degenerate and are resorbed, and that all the definitive ova arise after birth from the germinal epithelium.
NUMBER OF OVA! ALBINO RAT 439
From these references we see how diverse are the opinions regarding the new formation of the oocytes; Van Beneden, LaneClay pon, Winiwarter and Sainmont beheving in a new formation of ova after birth in some mammals, and Van der Stricht considering the definitive ova to be developed from the second proliferation of the germinal epithelium, meaning probably a new formation of ova after birth. On the other hand, Kingsbury and Felix find no evidence of the new formation after birth. Lastly, Kingery concludes after birth that a new formation of ova occurs from the germinal epithelium and these in turn form the definitive ova.
As far as my observations go, the new formation of germ cells from the germinal epithelium occurs at ten to fifteen days after birth, and this new formation is much more active in the period from fifteen to sixty days — i.e., up to puberty — but after puberty the process becomes slow, differing from that found in the mouse.
Thus my own observations on the rat agree with the observation of Kingery that there is a new formation of the germ cells from which the definitive ova originate. ,
In chart 2 the total number of ova, which include the primitive germ cells, formed in embryonic life, and the definitive ova, socalled second postnatal proliferation of the germ cells from the germinal epithelium, are shown, but it would be impossible to determine the relative number of the primitive germ cells and the definitive ova, owing to the lack of structural characters differentiating these two kinds of ova, at a glance, while counting.
In chart 2 also two characteristic features are shown between four and sixty-three days, and I have attempted to interpret these in the following way:
From four days after birth the total number of ova decreases very rapidly up to twenty-three days. This rapid decrease is probably due to the degeneration and resorption of the primitive germ cells. But even during this period of rapid fall the formation of the new germ cells is going on since these are found from ten days of age. However, on account of the much greater number of the degenerating cells, the graph inevitably shows a rapid
440 HAY A TO AEAI
fall. Following this rapid fall, the next period is represented by one of constancy from about twenty-three up to about sixtythree days. This period of constancy may be due to a balance between the degenerating cells on one hand and the newly formed germ cells on the other. Among the degenerating germ cells may be some of the germ cells of the second proliferation besides the primitive germ cells, and, though lacking evidence, I am inclined to believe that at this time the majority of the primitive germ cells have already disappeared.
The statements made by Winiwarter and Sainmont and by Kingery that all primitive germ cells are degenerated, and the view of the two former investigators that all of the second proliferated germ cells have disappeared, may very likely apply to this prepubertal period in the rat as mentioned above.
Following this period of constancy, the curve again shows a rapid decrease up to seventy days. Since during this period the corpora lutea begin to appear, we may assume that at this period also the cells are degenerating rapidly. Although even after puberty there is some new formation of oocytes, the sudden decrease in the number of ova must be due to a great excess of the degenerating cells.
Following this second rapid fall, the curve now shows a gradual decrease up to 947 days, though there occur some slight fluctuations, probably merely individual, especially at the earlier period. We may safely state that, though some few ova might be newly formed, the decrease in the total number of ova is due to the degeneration of the germ cells which represent those of the second proliferation.
I wish to emphasize the fact that the degeneration of the primitive germ cells begins from one day after birth and continues up to about sixty-three days, at which time all of the primitive ova may disappear completely — a result which in general agrees with the observation of Kingery.
Chart 2 also shows that the larger oocytes are relatively more numerous at an earlier age than at puberty.
This relation msiy indicate that the primitive ova before puberty, especially at the earlier period, enlarge rapidly, and before
NUMBER OF OVA: ALBINO RAT 441
ripening may undergo degeneration and be resorbed. From thirty days on the prohferated definitive ova are added to the primitive germ cells which are already present, and thus the definitive ova are very few at first, but increase rapidly concomitantly with the degeneration of the primitive germ-cells. This process maintains an approximately constant number of the larger oocytes, and this continues with more or less fluctuation up to 947 clays.
The effect of pregnancy on the total number of ova is given in table 4, but the number of instances is too small to furnish a basis for any general statement.
Stratz ('98) considers that during pregnancy there are small follicles which become atretic before they can develop, and only toward the end of pregnancy the follicles begin to grow to a considerable size and come to maturity. On the other hand, Loeb ('11) maintains that while some of the large follicles degenerate, the small, medium, and some of the large follicles also remain without degeneration in the last days of pregnancy.
According to my own observations, the condition of the follicles as a whole agrees with part of the statements given by the two authors mentioned above, though differing in detail. During pregnancy in young rats the small follicles are few compared with the medium and large follicles. In the later stages of pregnancy in older rats the relative number of small follicles increases considerably (table 4), while the numbers of the medium and large-sized follicles are considerably reduced when compared with those found in non-pregnant rats of about the same age.
We infer from these facts that in pregnancy in older rats the majority of the medium and large-sized follicles have degenerated. However, this statement is based on a limited number of cases, and, in addition, cytological studies on the cells were not made, so that no great emphasis can be put on the conclusion. It is my hope to continue the study on these problems in the future.
THE AMERICAN JOURNAL OF ANATOMY, VOL 27, NO 4
442 HAYATO ARAI
On the weight of the ovaries and the presence of corpora lutea and
of degenerate follicles
The graph for the number of ova which illustrates the group in which the ovaries possess the corpora lutea, gradually falls, with some fluctuations, from 21.3 to 78 mgm. in the weight of the ovaries (chart 4) .
The two graphs which illustrate the numbers of corpora lutea show rather considerable fluctuations, but indicate that the number of small, increases more rapidly than the number of large corpora lutea — a result which is in accord with expectation. In this (b) group, then, the relation between the weight of ovaries and the ova number is also inverse, though it is not so striking as in the (a) group, and the inverse relation is due in some measure to the appearance of the corpora lutea.
It is desirable now to discuss the influence which the number of degenerate follicles may have on the weight of the ovaries. Previously it was mentioned that an effort had been made to divide the degenerate follicles into four groups (p. 409).
However, on account of the great difficulty in making even an approximate estimate of the number of the small degenerated follicles, I have not attempted to record these in the table. For convenience, the number of the C and D types of my classification, or those which correspond to large degenerated follicles, and the 13 type, or the middle-sized degenerated follicles, are grouped together and the results given in table 13.
Table 13 suggests that in the rat before puberty the weight of ovaries, in which the large degenerated follicles are the more numerous, tend to be greater than that of the ovaries in which these are less numerous. After puberty, though the similar relation seems to hold, nevertheless the presence of the corpora lutea obscures the relation. Generally speaking, in the ovaries of young rats (twenty-six days old) before the corpora lutea are formed, we find a considerable number of large degenerated follicles.
From table 13 it is clear that before the formation of the corpora lutea the number of these follicles decreases slowly with the
NUMBER OF OVA! ALBINO RAT
443
increase in the weight of both ovaries. When the corpora lutea do appear, the number of large degenerated folUcles remains about the same (namely, twenty-seven) from sixty-seven up to 133 days, but after that period is reduced to about half, namely, fifteen, and this value is maintained up to 506 days. At 947 days, however, the number of large degenerated follicles becomes onl}^
TABLE 13
The relation between the weights of both ovaries and the middle-sized and large degenerate follicles, arranged by age in days; the average number
NUMBER OF RATS
INTERVAL OF AGE
AGE
WEIGHT OP BOTH OVARIES
NUMBER OF DEGENERATE FOLLICLES
Middle
Large
Total
Rats without corpora
lutea
days
days
mgvi.
1
26
10.8
9
92
101
3
30-36
34
7.6
63
44
107
3
41-46
43
11.8
56
35
91
4
50-64
56
10.6
36
19
55
2
80-95
87
■ 10.8
36
26
62
2
100-110
105
13.8
33
12
45
Rats with corpora lutea
2
64-70
67
37.4
55
26
81
2
80-84
82
29.8
21
28
49
2
95-100
97
46.8
32
27
59
3
110-150
133
41.1
32
28
60
3
198-262
222
53.9
22
13
35
2
318-385
352
59.6
17
16
33
2
454-559
506
53.7
24
17
41
1
947
65.2
4
6
10
six, yet the weight of the ovaries is 65.2 mgm. Similar relations appear when the numbers of degenerated follicles are arranged according to the weight of both ovaries instead of age.
As was already stated, the precise number of small degenerated follicles is hard to determine on account of the lack of any distinct character, such as the presence of a nucleus in the ovum. However, some notion of even an approximate number is highly desirable.
444
HAYATO ARAI
The number of these small degenerated follicles in the ovaries without corpora lutea lies between 300 and 900, while in the ovaries with corpora lutea their number varies from 600 to 1400. It is a remarkable fact that the number of these small follicles is not particulai'ly different in the ovaries of pregnant as compared with the non-pregnant rats. Often in the ovaries in which corpora lutea are not present the small degenerated follicles are abundant, as, for instance, in the rat at 110 days, in which the number was 1500. Also in the ovaries with corpora lutea the number of small degenerated follicles may be very small, as in the rat at seventy days, in which it was 300. The average num
TABLE 14
Tabulation of degenerated follicles
SMALL
MIDDLE-SIZED
LARGE
TOTAL NUMBER
Fourteen eases without corpora lutea
Sum
6,734
484
651 46
460 33
7.845
Average
563
Seventeen cases with corpora lutea
Sum
14,280 840
463
27
357 21
5,100
Average
888
bers of the different sized degenerated follicles in all cases are shown in table 14.
Ovulation
In regard to the ovulation of mammals, as well as the maturation of the ova, there are numerous observations. It is generally held that the maturation process takes place only as the result of a specific stimulus which may follow copulation or the entry of the spermatozoon into the oviducts. Yet there are also numerous observations which show that the maturation process may take place independently of any such stimulus. For instance, Weil (73) in the rabbit, Sobotta ('95) in the mouse, Tafani ('89)
NUMBER OF OVA: ALBINO RAT 445
in the rat, and Rubaschkin ('05) in the guinea-pig, stated that ovulation occurs spontaneously during heat and is independent of coitus. Iwanoff ('00) showed that in the rabbit pregnancy is also possible by the artificial insemination, and Heape ('97) tried artificial insemination on mares, donkeys, and cows, and succeeded in producing pregnancy in all.
Loeb ('11) also believes that in the guinea-pig ovulation occurs in the large majority of cases independently of copulation. Marshall and Jolly ('05), in the dog and in the ferret, described the spontaneous ovulation at each of the earlier heat periods during the breeding season.
To test this matter in the albino rat, I used the control females employed in a study of the surviving ovary after semispaying. These control female rats were separated from the males at twenty days of age, and were kept together with the semispayed rats of the same litter. Nevertheless, in the ovaries of these two control rats were found corpora lutea at sixty-two and sixtynine days, respectively; that is, ovulation occurred spontaneously without any association with the male. From all these results there is little doubt that in the majority of mammals ovulation occurs regularly during the oestrus period and is independent of copulation.
Although many investigators have studied the relation between menstruation and ovulation in the higher mammals, such as the monkey and man, yet whether ovulation occurs before, during, or after menstruation has not been determined. It follows, therefore, that at least in monkeys, as well as in man, the process of ovulation does not seem to be necessarily associated with menstruation, though such a statement is not definitely made by most of the observers.
According to Heape ('98), ovulation and menstruation are not associated, since in monkeys menstruation may occur periodically all the year round, but the season for ovulation and conception is limited. Van Herwerden ('06) has also given further evidence that there is no close connection between ovulation and menstruation, either in monkeys or in the aberrant lemur, Tarsius spectrum.
446 HAYATO ARAI
In the case of the human female there are several opinions as to the usual time for the discharging of the o\Tim. Some authors report that ovulation occurs before menstruation; others, during that process, and still others, that it follows menstruation.
Hergesell ('05) holds that ovulation precedes menstruation for the reason that the most usual period for ovulation in the human female, as in many of the lower mammals, w^as during a definitive oestrus following the preoestrus; for the period of most active sexual feeling is generallj^ just after the close of the menstrual period, while, according to Raciborsky (Traite de Menstruation: cited from Physiology of reproduction, Marshall," '10), this is also the commonest season for fertile coition. Contrary to this, Bryce and Teacher ('08) hold that the ovimi is discharged shortly after the cessation of the last menstruation.
Touching the question whether a special stimulus induces ovulation in w^oman, Oliver ('02) regards the view that coitus accelerates ovulation as the more probable, since at this time there is an increased blood supply to the whole genital tract. Heape ('05), however, maintains that the cause which determines the rupture of the Graafian follicle is, in the rabbit, the stimulation of erectile tissue, due to a nervous reflex, and not simply the result of internal pressure arising from an increased blood supply or a greater quantity of liquor folliculi.
Harper ('04), in pigeons, concludes that ovulation requires only a slight stimulus, 'mental,' and that the presence of sperm in the oviduct cannot be regarded as important. Kolliker ('02) considers the cause of rupture as a simple mechanical process because the irritation of vasomotor nerves increases the pressure of the liquor folliculi thus inducing the rupture.
From the foregoing, it is evident that the real cause of the rupture of the Graafian follicle is not clearly established, and therefore that the factors which may induce ovulation require further study.
Whatever may be the final conclusion as to the cause, it is clear that ovulation is closely related to the maturing of the ovary, as my present study indicates.
NUMBER OF OVA: ALBINO RAT 447
As was shown in table 2, during relatively early stages, for instance at twenty days after birth, many follicles containing ova from 40 to 60 /x or more in diameter were found, and again in the rat at twenty-six days after birth there were found large numbers of well-developed follicles, which cannot be differentiated from mature follicles by mere examination (table 2) ; yet, despite the presence of these larger follicles, there is no evidence of ovulation in these younger rats.
Runge ('06) stated that enlarged follicles are by no means uncommon in ovaries of young children. In the first year of life he found follicles of considerable size, and in the second year still larger ones, some having a diameter of 135 ^(. In the third year degenerate follicles were also found, and he concluded that the maturing of the follicles begins early. Loeb ('11) also found in the guinea-pig, eighteen days old, relatively large follicles in the ovaries which were yet small in size.
Though to my regret I have not studied the relation between the stroma and the development of the ovaries, or the internal secretion of the ovaries and its relation to their development, yet the observations of many investigators, as well as my own, indicate that the period of puberty is induced principally by the ripening of the ova in the follicles.
In the absence of coitus it is difficult to detect any special stimulus as the cause of the first ovulation or those which follow. It naturally suggests itself that influences arising outside of the ovaries may determine the rupture of the mature follicles, and one turns to the various glands associated with the reproductive system as possibly concerned. Thus the hypophysis and suprarenal glands in albino rats are larger in the female than in the male, the differences in size between the two sexes appearing usually somewhat before puberty (Hatai, '13), thus indicating greater activity at that time.
Again, the hypophysis has an intimate relation with the reproductive organs. It is also known that the thyroid changes in size during menstruation in man, and in the mammary glands, according to the recent studies of Myers ('16) on the rat, the branching of the ducts goes on at an unusually rapid rate about
448 HAYATO ARAI
the ninth week, which probably corresponds to the age of puberty. Myers did not discuss the relation of this rapid growth to puberty. The suggestion is that these various organs might be, some or all of them, related to the process of ovulation in the sense of forming stimulating substances causing ovulation, and it is my hope to make further studies along this line in the future.
Corpora lutea
I now wish to consider the relation between the first appearance of corpora lutea and puberty.
For this purpose I have assembled the data from seventy-nine albino rats, ranging in age from thirty days up to about thirtytwo months. For some of them the weights of the ovaries were not determined.
As is shown in table 15, the corpora lutea first appear in a rat at sixty-one days, but after sixty-one days, though corpora lutea are present in most cases, they are not present in all. The absence of the corpora lutea in the rats after sixty-one days is always associated with a body weight too small for the age, showing poor nutrition. The weights of the ovaries are also small.
I have next rearranged some of the data, given in table 15, according to the body weights of rats, omitting those with body weights less than 75.5 grams and greater than 113.5 grams (table
16).
We notice the first appearance of the corpora lutea in the rats with a body weight of 78.5 grams, but they are not always present until the rats reach 100 grams in body weight.
Beyond 100 grams we always find corpora lutea in ovaries. So far, then, as the body weight is concerned, the first appearance of the corpora lutea occurs at from 78.5 up to 100 grams. These body weights of 78.5 to 100 grams correspond to sixty-one and seventy-one days, respectively, as given in Donaldson's table. Thus in my series the appearance of puberty approximately coincides with the observation of Donaldson ('15). From these data it appears that while puberty is attained as a rule between sixty-one to seventy-one days in rats that have grown approxi
NUMBER OF OVA: ALBINO RAT
449
TABLE 15
The relation between the corpora lutea and the age, body weight and body length
AGE
BODY WEIGHT
BODY LENGTH
WEIGHT or BOTH OVARIES
CORPORA
LUTEA
AGE
BODY WEIGHT
BODY
LENGTH
WEIGHT OF BOTH OVARIES
CORPORA
LUTEA
days
grams
mm.
mgm.
days
grams
mm.
mgm.
30
34.8
108
6.4
—
91
125.7
180
55.6
+
36
34.9
105
5.6
—
91
131.8
176
45.7
+
36
50.0
122
10.4
—
91
93.5
158
57.1
+
41
58.2
131
7.4
95
72.0
146
—
41
61.9
128
14.0
—
95
67.9
132
—
50
74.6
146
11.2
^__
95
98.5
148
12.2
—
50
75.5
144
12.9
—
95
160.0
182
73.5
+
60
93.5
145
10.3
—
100
78.5
138
8.8
—
61
80.5
153
23.0
+
100
97.8
156
20.1
+
62
84.0
152
30.8
+
102
95.0
150
+
62
120.9
169
36.6
+
102
132.5
171
+
64
62.7
132
7.9
—
110
94.3
147
18.9
—
64
113.5
165
31.1
+
110
167.1
185
41.6
+
65
77.2
145
12.2
—
112
86.5
148
—
69
78.5
148
40.5
+
112
95.8
152
+
69
88.8
154
34.1
+
112
122.8
164
+
69
90.0
154
23.5
+
130
122.3
170
42.8
+
70
106.3
162
43.8
+
130
103.3
158
38.8
+
74
87.3
154
22.1
+
140
123.0
168
49.2
+
74
111.7
163
34.5
+
141
140.5
175
33.8
+
75
91.7
155
22.7
+
150
129.5
171
32.5
+
75
97.9
156
23.0
+
170
130.5
173
28.0
+
79
119. S
166
34.9
+
172
124.6
178
31.7
+
80
77.3
140
9.4
—
179
130.0
173
26.2
+
80
107.3
153
37.4
+
181
150.3
173
53.9
+
82
41.9
118
—
181
156.3
194
50.8
+
82
58.0
125
—
194
100.0
148
15.1
—
82
73.1
141
—
194
90.3
145
14.2
—
82
58.6
128
—
198
142.7
171
58.1
+
82
65.0
132
—
206
188.5
185
54.8
+
83
47.6
118
262
145.0
185
48.9
+
83
82.0
147
315
190.8
193
53.1
+
84
48.5
125
318
155.0
189
38.5
+
84
61.0
132
—
385
161.3
194
82.6
+
84
41.1
114
—
454
138.7
194
33.8
+
84
55.5
127
' —
559
198.9
200
73.5
+
84
64.5
124
—
947
238.0
215
65.2
+
84
125.0
165
22.2
+
86
59.5
125
—
86
70.5
135
—
86
60.0
132
—
88
88.6
150
"^
450
HAYATO ARAI
mately normalh^, yet malnutrition as represented bj'- a deficient body weight may delay its appearance or even entirely prevent it. This is in accord with laboratory observations on breeding.
TABLE 16
The relation between the corpora luiea and the body weight. Body, weight, 75 to
115 grams
AGE
BODY WEIGHT
BODY LENGTH
WEIGHT OF BOTH OVARIES
CORPOUA LUTEA
days
grams
mm.
mgm.
50
75.5
144
12.9
—
65
77.2
145
12.2
—
80
77.3
140
9.4
—
69
78.5
148
40.5
+
100
78.5
138
8.8
—
80.0
148
+
61
80.5
153
23.0
+
83
82.0
147
—
62
84.0
152
30.8
+
112
86.5
148
—
74
87.3
154
22.1
+
88
88.6
150
—
69
88.8
154
34.1
+
69
90.0
154
23.5
+
194
90.3
145
14.2
—
75
91.7
155
22.7
+
60
93.5
145
10.3
—
91
93.5
158
57.1
+
110
94.3
147
18.9
—
102
95.0
150
—
112
95.8
152
+
100
97.8
156
20.1
+
75
97.9
156
23.0
+
95
98.5
148
12.2
—
194
100.0
148
15.2
—
130
103.3
158
33.8
+
70
106.3
162
43.8
+
80
107.3
153
37.4
+
113.0
167
+
64
113.5
165
31.1
+
Finally, I have arranged the data given in table 15 according to the body length of the rats. Rats whose body lengths are less than 145 mm. and greater than 155 mm. have been eliminated, and the results are shown in table 17.
NUMBER OF OVA.' ALBINO RAT
451
As is seen in the table, the first appearance of corpora lutea takes place in the ovaries of a rat having a body length of 148 mm. From 148 mm. to 155. mm. we find but one exception in which the rat is notably short for its age. The body length of 148 mm. to 150 mm. coincides with the age of sixty-two to sixty TABLE 17
The relation between the corpora lutea and the body length. Body length 14-5 to
155 mm.
AGE
BODY WEIGHT
BODY LENGTH
WEIGHT OP BOTH OVARIE.9
CORPORA LUTEA
days
grams
mm.
mgm,.
60
93.5
145
10.3
—
65
77.2
145
12.2
—
194
90.3
145
14.2
—
50
74.6
146
11.2
■~
95
72.0
146
—
83
82.0
147
—
110
94.3
147
18.9
—
95
98.5
148
12.2
—
194
100.0
148
15.1
—
112
86.5
148
—
69
78.5
148
40.5
+
80.0
148
+
88
88.6
150
—
102
95.0
150
+
62
84.0
152
30.8
+
112
95.8
152
+
61
80.5
153
23.0
+
80
107.3
153
37.4
+
69
88.8
154
34.1
+
69
90.0
154
23.5
+
74
87.3
154
22.1
+
75
91.7
155
22.7
+
five days in Donaldson's table. In my rats, however, the corresponding ages are from sixty-nine to eighty-eight days, respectively. This disagreement between my own determination and that by Donaldson is undoubtedly due to the poor nutritional condition of the rats here employed. I therefore conclude that the body length is the best criterion among the three characters, age, body weight and body length, so far considered. I have
452
HAYATO ARAI
compared the results obtained by the three different methods in table 18.
It is at once clear from table 18 that when body length is taken as a criterion, the range at which period the corpora lutea first appear is least, namely, the age of sixty-two to sixty-five days.
Corpora lutea in pregnant and non-pregnant rats
In regard to the corpora lutea there are numerous observations, especially on their origin. Von Baer ('27) considers that the corpora lutea consist entirely of connective tissue, and in their formation the follicular epithelium has no share. On the
TABLE 18 Conditions determining the appearance of the first corpora lutea
THE METHOD OF COMPARISON
THE TIME OF FIRST APPEARANCE OF CORPORA
LUTEA
THE AGE IN DATS FROM DONALDSON'S TABLE ('15)
Bv age
62 to 110 days
78.5 to 100.0 grams
148 to 150 mm.
60 to 70
By body weight
By body length
61 to 71
62 to 65
other hand, Bischoff ('42) concluded that the luteal cells were formed by the hypertrophy of the epithelial cells of the undischarged Graafian follicles. Ever since these statements were made by Von Baer and by Bischoff they have been the subject of discussion.
Marshall ('10) stated that if the discharged ovum fails to become fertilized, the corpus luteum goes on growing for a short time and then degenerates. In the smaller animals it disappears after a comparatively short time. If, on the other hand, conception follows ovulation, the corpus luteum continues to increase in size until almost the middle of pregnancy.
Loeb ('11) also found in guinea-pigs that the corpora lutea which are formed without pregnancy are much smaller, and shrank more rapidly than those the formation of which was followed by pregnancy.
NUMBER OF OVA I ALBINO RAT 453
On the other hand, Sobotta ('06), from his study on the mouse, expressed the view that the persistence of the corpora lutea and their ultimate size are not altered by conception.
In the present study we have examined four pregnant rats, and found that, as Loeb described, the corpora lutea in the pregnant rats were larger than those in rats not pregnant. However, the difference is slight. The completely formed corpora lutea at about ten days after conception, judging from the size of the fetus, are about 2.7 mm. in diameter. This size has diminished to about 2.4 mm. in diameter about seventeen days after pregnancy, that is, in the later phase.
So long as I did not collect the material with a view to studying the fate of corpora lutea, I am unable to discuss their age. If, however, we divide the entire population of corpora lutea into two groups, the larger and the smaller ones, it is possible to study the influence of these on the weight of ovaries.
As is shown in tables 3, 6, 8, and 10, both the total number of the corpora lutea, as well as the number of small ones, show an unmistakable tendency to increase, despite great individual variation, according to the age or other measurements of the rats. On the other hand, the number of corpora lutea of large size remains approximately constant.
From these results we conclude that after puberty the accumulation of the smaller corpora lutea is mainly responsible for the increase in the weight of the ovaries with increasing age.
The degeneratio7i of the follicles
So far I have simply stated the relation which exists between the total number of ova and of the degenerated follicles; but I now wish to consider these degenerated follicles in their relation to the corpora lutea. As has been mentioned already (table 13), the degenerated follicles are not found in the rat until about twenty-six days. The failure to find any degenerated follicles up to this time may be due partly to the extreme difficulty in recognizing them and partly to a possible resorption immediately after they are formed. However this may be, after twenty-six
454 HAYATO ARAI
days the degenerated follicles were first found and these probablyoriginated from enlarged primitive follicles. % Loeb ('11), while studying the cyclic changes in the ovaries of guinea-pigs, found that at eighteen days of age the degenerative process in some follicles had been entirely completed, and connective tissue had begun to grow into the cavity. Thus the degenerative processes occur at about the same phase both in the rat and in the more precocious guinea-pig.
Moreover, Loeb states that, associated with ovulation, all the follicles, with the exception of very small ones, degenerate. The general degeneration of the follicular granulosa cannot be seen before ovulation. This sudden degenerative process, as well as tj^pical follicular degeneration, is quite independent of coitus. He further found that in newly ruptured follicles the degeneration of the granulosa is shown, except in the very small follicles, while in a large majority of the follicles almost the whole granulosa is found in the process of degeneration, and this degeneration is essentially independent of copulation and of pregnancy, but directly connected with ovulation. Furthermore, from the age of the corpora lutea, the ultimate fate of the follicles, i.e., whether these will disappear or not may be inferred. At a given time, approximately ten days after ovulation, a certain equilibrium is reached between the follicles which undergo degeneration and those which grow further. Among those which were growing, the degenerative process may also take place.
Though in my study the exact age of the corpora lutea cannot be determined, we can assume for the two pregnant rats, whose ages are eighty and ninety-five days, respectively, that the corpora lutea (from the estimated age of the fetus) were formed within the ten preceding days. In these cases the number of the degenerated follicles of middle and large sizes is far greater than in the other rats at about the same age. Although in these cases the corpora lutea may have been present within ten days after ovulation, as was inferred, yet it is premature to conclude from my study that all of the follicles of large and medium size undergo degeneration after the appearance of relatively new corpora lutea, as Loeb stated. The number of middle-sized
NUMBER OF OVA! ALBINO RAT
455
and large degenerate follicles is about the same, whether the ovaries contain new or old corpora lutea. Although there are slight differences before or after puberty, as shown by the average values of their numbers — 74 and 49, respectively.
As was mentioned already (p. 444), the number of small degenerated follicles shows large fluctuations — between 300 to 900 — in ovaries without corpora lutea, and thus an accurate determination of degenerated small follicles is very difficult. However, it seems certain that after puberty the number of degenerated small follicles increases from about 600 to 1400. The average number of fourteen cases before puberty gives 563 small follicles, while the average number of seventeen cases after puberty is increased to 888. The average number of all thirty
TABLE 19
Nimibers of degenerated follicles before and after puberty
Before puberty . After puberty . .
lEAN OP THE TOTAL NUMBER OF OVA
9380 5592
AVERAGE NUMBER
or ALL DEGENERATE
FOLLICLES
637 933
THE PERCENTAGE OF
DEGENERATE
FOLLICLES TO TOTAL
NUMBER OF OVA
6.79 16.66
one cases is therefore 740 follicles. To this, the mean number of fifty-nine medium and large degenerated follicles are to be added, so that we obtain about 800 as the total number.
In table 19 the proportion of these degenerated follicles to the total number of ova is shown.
It is reasonable to conclude from all the data (tables 2 and 4) that before puberty the number of the large degenerate follicles is one and a half times that found in the ovaries of rats after puberty, while we have already found that the number of small degenerate follicles after puberty is one and a half times that found before puberty.
Loeb ('06) described the small follicles as always present after either ovulation or the appearance of the corpus luteum. My own data, however, show that after puberty, that is after the appearance of corpora lutea, the number of small degenerated fol
456 HAYATO ARAI
licles is considerably increased as compared with their number before puberty. This finding is different from that of Loeb, but the difference may be due partly to the difference in the animals used. However, it seems to me more probable that the appearance of the corpora lutea gives an impulse to the degeneration of the small follicles.
At any rate, the .percentage of degenerated follicles after puberty is higher than before puberty, as is shown in the above calculation, where the number of degenerated follicles is as high as about 16 per cent of the total number of ova. Therefore, the decrease in the number of ova according to the age seems to be caused principally by the degenerated follicles. We can neglect the ripened ova, eight to ten of which are discharged into the oviducts at every ovulation period, as this number is insignificant in relation to that of the degenerate follicles.
Sobotta and Burckard ('10) stated that in white rats the maximum number of ripe ova which enter the oviducts is altogether thirteen from both ovaries and the minimum is four, although eight to ten ova are more usual. The maximum number of ripe ova from one ovary is said to be eight.
According to Donaldson, the largest litter noted in the common albino is seventeen, while Kolazy ('71) also reported a litter consisting of seventeen young.
According to these observations, the highest number of ova discharged into the fallopian tubes is seventeen and the lowest is four. Usually it is eight to ten. The average number of the mature follicles in the ovaries at several ages, however, is twentyone, and therefore about half of these mature follicles must rupture and discharge their ova into the oviducts, and the remaining half must undergo atresia.
NUMBER OF OVA! ALBINO RAT 457
Comparison between man and the rat in regard to the postnatal
changes in the ovaries
It may be worth while to compare the results obtained from these studies on the development of the ovary in the rat with those in man, especially during the period in which the degeneration of the primitive germ cells and the new formation of definitive ova is most active.
If we take sixty-five days as the mean age for the first ovulation, we find that the rat is distinctl}^ precocious for sixty-five days, corresponds to about sixty-five months of human life, or roughly, five and a half years. According to Vierordt's table, the first menstruation in man may occur in tropical countries at eight years, but more commonly a year or two later.
On the other hand, the cessation of the breeding period in the female rat at eighteen to twenty months ( = 45 to 50 years) agree very well with the appearance of the menopause which occurs in man between forty-five and fifty years.
As is to be expected, individual rats may breed for a longer period, and King ('15) has reported a female bearing a litter of one at twenty-two months and, as table 15 shows, the rat at 947 days ( = thirty-one months) had newly formed corpora lutea in its ovaries.
SUMMARY
1. The total number of ova in both ovaries was counted in thirty-nine albino rats ranging in age from birth to 947 days.
2. In relation to the body weight the size of the ovaries increases to a maximum at 33 grams of the body weight, then decreases up to puberty, after which it increases rapidly and reaches the second maximum.
The ovary weight according to age shows continuous increase up to thirty-one months (table 12).
3. The weight of the right ovary is less than that of the left — ■ alDout 90 per cent — while the total number of ova in the right ovary is slightly more than in the left, though the difference is small (table 1).
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, NO. 4
458 HAYATO ARAI
4. In general the numl)er of ova decreases with age. The total number of ova in both ovaries decreases rapidly from 35,100 at birth to about 11,000 at twenty-three days. From twentythree to sixty-three days the number is nearly constant (11,000 to 10,000). It then decreases again rapidly (to about 6600) at seventy days. During this last period ovulation usually occurs. From seventy days up to the thirty-one months there is a slow decrease to about 2000 ova. In general, this decrease results mainly from the degeneration of the primitive ova, but in part from that of the definitive ova (tables 2 and 3, charts 1 and 2).
5. In non-pregnant rats the percentage of larger-sized ova to the total number remains nearly constant. In young pregnant' rats the percentage of ova more than 20 fj. in diameter is greater than in the non-pregnant rat, but in older pregnant rats this percentage decreases. These conclusions are, however, based on four instances only.
6. The graphs illustrating the change in the total number of ova are similar in form whether they are based on the body weight or the body length (table 6, chart 3).
7. With the increasing weight of the ovary the total number of ova decreases. The increase in weight is associated before puberty principally with the formation of large degenerate follicles together with mature follicles and growth of connective tissue, but after puberty the increase depends mainly on the accumulation of small corpora lutea in addition to the mature and degenerate follicles and connective tissue. After puberty the number of large corpora lutea is about the same in all ovaries, and these, therefore, are not responsible for the regular age changes in the weight of ovaries (table 10, chart 4).
8. In albino rats the new formation of the egg cells takes place after birth from the germinal epithelium. These ova grow in situ and, as development proceeds, are covered by the adjacent epithelial cells and extend into the stroma, passing through the tunica albuginea. From these newly formed germ cells the definitive ova appear to develop, beginning from about the second week after birth, and the formation of them is most active in the period between the third and ninth weeks. During puberty
NUMBER OF OVA: ALBINO RAT 459
this new formation becomes less active, though it may continue for a year after birth (chart 2) .
9. The primitive ova, which are present during foetal Ufe, are found degenerating immediately after birth. The rate of degeneration rapidly diminishes from birth to three weeks of age, but continues up to sexual maturity, at a slower rate. The exact period of degeneration of definitive ova is not known, but probably it begins before puberty, and after puberty the degenerate follicles are derived principally from the definitive ova. In the rat about four weeks old the medium-sized follicles show degeneration, and in general the number of degenerated follicles of large size is more than one and a half times that found before puberty. The converse relation is true in the case of small follicles. The mean number of all degenerated follicles is about>10 per cent of the total number of ova.
10. Ovulation can occur spontaneously, independent of sexual intercourse and without the influence of the male sex. Welldeveloped follicles appear as early as twenty-six days after birth. These follicles contain ova with a diameter of 60 ^( — equal to those found in well-developed mature follicles. Should some special stimulus be deemed necessary for the discharge of the ovum, it is suggested that either the ovary itself or some other ductless gland might furnish such an hypothetical stimulating substance.
11. The body length of rats was found a better criterion for the first appearance of corpora lutea than either age or body weight. The corpora lutea are found in rats between 148 to 150 mm. in body length (table 18).
12. The corpora lutea formed in rats in which the ova have been fertilized are a little larger than those in non-fertilized rats. It is stated that usually eight to ten ripened ova are discharged at the same time. We found, however, that near maturity there may be as many as twenty-one follicles in both ovaries.
460 HAYATO ARAI
LITERATURE CITED
Allen, B. M. 1904 The embryonic development of the ovary and testis of the
mammals. Am. Jour. Anat., vol. 3. VON Baer, C. E. 1827 De ovi mammalium et hominis genesi. L. Vossii, Lip siae. VAN Beneden, E. 1880 Contribution a la connaissance de I'ovaire des mam miferes, etc. Arch. d. Biol., T. 1. BiscHOFF, T. L. W. 1842 Entwickelungsgeschichte des Kanninchen-Eies.
Braunschweig, F. Vieweg u. Sohn, 154 pp. Bryce, T. H., and Teacher, J. H. 1908 Contributions to the study of the early
development and imbedding of the human ovum. Glasgow. Donaldson, H. H. 1906 A comparison of the white rat with man in respect
to the growth of the entire body. Boas anniversary volume.
1915 The rat. Reference tables and data for the albino rat (Mus
norvegicus albinus) and the Norway rat (Mus norvegicus). Memoirs
of The Wistar Institute of Anatomy and Biology, no. 6. DusTiN, A. P. 1907 Recherches sur I'origine des Gonocytes chez les Amphi biens. Arch, de Biol., T. 21. Felix, W. 1912 The development of the urinogenital organs. In Manual of
Human Embryology. Keibel and Mall, vol. 2. J. B. Lippincott Co.,
Phila. FiRKET, Jean 1920 On the origin of germ cells in higher vertebrates. Anat.
Rec, vol. 18, pp. 309-316. VON Hansemann, D. 1913 tjber den Kampf der Eier in den Ovarien. Archiv
flir Entwcklngs. der Organismen, Bd. 35. Harper, E. H. 1904 The fertilization and early development of the pigeon's
egg. Am. Jour. Anat., vol. 3. Hatai, S. 1913 On the weights of the abdominal and the thoracic viscera, the
sex glands, ductless glands and the eyeballs of the albino rat (Mus
norvegicus albinus) according to body weight. Am. Jour. Anat., vol.
15.
1914 On the weight of some of the ductless glands of Norway and of
the albino rat according to sex and variety. Anat. Rec, vol. 8. Heape, W. 1897 The artificial insemination of mammals and subsequent possible fertilization or impregnation of their ova. Proc. Roy. Soc. London, vol. 61.
1898 The menstruation of semnopithecus. Trans. Obstet. Soc, vol.
40.
1905 Ovulation and degeneration of ova in the rabbit. Proc. Roy.
Soc. London, vol. 76 B. Henle, J. 1873 Handbuch der systematischen Anatomic des Menschen. Bd.
2, 2 Aufl., S. 504. Braunschweig. Hergesell, G. 1905 Das zeitliche Verhalten der Ovulation zur Menstruation.
Inaug. Diss., Leipzig. van Herwerden, M. 1906 Bijdrage tot de kennis van den menstrueelen cyclus.
Tijdschr. nederl. dierk. Vereen, vol. 10.
NUMBER OF OVA: ALBINO RAT 461
Heyse, G. 1897 Einige Beitrjige zur mikroskopischen Anatomie der Ovarien
Osteomalatischer. Arch, fiir Gynakologie, Bd. 53, S. 334. d'Hollander, F. G. 1904 Recherches sur I'oogenese et sur la structure et la
signification du noyau vitellin de Balbiani chez les Oiseaux. Arch.
Anat. Microsc, T. 7. IwANOFF, E. 1900 La fonction des vesicles seminales et de la glande prosta tique. Jour, de Phys. et de Path. Gen., T. 2. Jackson, C. M. 1913 Postnatal growth and variability of the body and of the
various organs in the albino rat. Am. Jour. Anat., vol. 15, p. 40. Jenkinson, J. W. 1913 Vertebrate embryology. Clarendon Press, Oxford, 267
pp. JoESSEL, G. 1899 Lehrbuch der topographisch-chirurgischen Anatomie. Zwei ter Theil fortgesetzt von W. Waldeyer, p. 793. Friedrich Cohen, Bonn. Karchakewitsch 1908 tjber den Ursprung des Urgeschlechtszellen bei Rana
escul. Sitzber. d. mat. -phys. Kl. d. Bayer Ak. d. Wiss., Bd. 38. King, H. D. 1915 On the normal sex ratio and the size of the litter in the
albino rat (Mus norvegicus albinus). Anat. Rec, vol. 9. Kingery, H. M. 1917 Oogenesis in the white mouse. Jour. Morph., vol. 30. Kingsbury, B. F. 1913 The morphogenesis of the mammalian ovary: Felis
domestica. Am. Jour. Anat., vol. 15. Kirkham, W. B. 1916 The germ cell cycle in the mouse. Abstract in Anat.
Rec, vol. 10, p. 217. KoLAZY, J. '1871 Ueber die Lebensweise von Mus rattus, varietas, alba. Ver handl. Zool. Bot. Gesellsch. Wien. KoLLiKER, A., UND V. Enner, V. 1902 Handbuch der Gewebslehre d. Menschen.
Bd. 3, 6. umarbeitete Aufl., S. 553-554 and 557. Lane-Claypon, Janet E. 1905 On the origin and life history of the interstitial
cells of the ovary in the rabbit. Prov. R. Soc. London, vol. 77 B. LoEB, L. 1906 The formation of the corpus luteum in the guinea-pig. J. of
Am. Med. Assoc, February 10th.
1911 The cyclic changes in the ovary of the guinea-pig. Jour. Morph.,
vol. 22. Marshall, F. H. A., and Jolly, W. A. 1905 Contributions to the physiology
of mammalian reproduction. Phil. Trans. Roy. Soc. Series B, vol. 198. Marshall, F. H. A. 1910 The physiology of reproduction. Longmans, Green
& Co., N. Y., pp. 134-140. Minot, Charles S. 1892 Human embryology, page 49. William Wood & Co.,
N. Y. Myers, J. A. 1916 Studies on the mammary gland. Am. Jour. Anat., vol. 19,
p. 379. Oliver, J. 1902 A study of fertilisation with reference to the occurrence of
ectopic pregnancy. Edin. Med. Jour., vol. 54. Raciborsky, a. 1868 Traite du menstruation. Paris, J. B. Bailliere et Fils. Riddle, O. 1918 Further observations on the relative size and form of the
right and left testes of pigeons in health and disease and as influenced
by hybridity. Anat. Rec, vol. 14. RUBASCHKIN, W. 1905 Ueber die Reifungs und Befruchtungsprozesse des Meer schweincheneies. Anat. Hefte, Bd. 29.
462 HAYATO ARAI
RuNGE, E. 1906 Beitrag zur Anatomie der Ovarien Neugeborener und Kinder
vor der Pubertatszeit. Arch. Gymik., Bd. 80. Sappey, p. C. 1879 Traito d'.anatomio descriptive. T. 4, pp. 720-721. Paris,
V. Adrien Delahaye et Libraires-Editeurs. Skrobansky, K. v. 1903 Beitriige zur Kenntnis der Oogenese bei Saugetieren.
Arch. f. mikr. Anat., Bd. 62. SoBOTTA, J. 1895 Die Befruchtung und Furchung des Eies der Maus. Arch.
f. mikr. Anat., Bd. 45.
1906 Ueber die Bildung des Corpus luteum beim Meerschweinchen.
Anat. Hefte, Bd. 32. SoBOTTA, J., UND BuRCKHARD, G. 1910 Reifung und Befruchtung des Eies der
weissen Ratte. Anat. Hefte, Bd. 42, p. 444. SoNNENBRODT 1908 Die Wachstumsperiode der Oocyte des Huhnes. Arch. f.
mikr. Anat., Bd. 72. Stratz, C. H. 1898 Der geschlechtsreife Siiugethiereierstock. M. Nijhoff,
Haag. VAN DER Stricht, R. 1911 Vitellogenese dans I'ovule de Chatte. Arch. Biol.
T. 26. Tafani, a. 1889 La fecondation et la segmentation. Etudiees dans les oeufs
des rats. Arch. Ital. de Biol., vol. 11. ViERORDT, H. 1906 Daten und Tabellen fi'ir Mediziner. 3 Aufl. Gustav
Fischer. Jena. Waldeyer, W. 1906 Die Geschlechtszellen. In "Handbuch der vergleich enden und experimentellen Entwickelungslehre der Wirbeltiere," by
Oskar Hertwig, erster Band, erster Teil, erste Halfte, S. 351. Weil, C. 1873 Beitriige zur Kenntnis der Befruchtung und Entwickelung des
Kannincheneies. Wien Med. Jahrbuch. WiEDERSHEiM, R. 1897 Elements of the comparative anatomy of vertebrates.
2nd ed. Trans, by W. N. Parker. Macmillan, London, p. 368. VON Winiwarter, H., et Sainmont, G. 1908 Nouvelles recherches sur I'ovo genese et I'organogenese de I'ovaire des mammiferes (chat). Arch.
Biol., T. 24.
1908 Ueber die ausschliesslich postfetale Bildung der definitiven Eier
bei der Katze. Anat. Anz., Bd. 32.
Resumen por el autor, Leon Augustus Hausman. Universidad Cornell, Ithaca.
Investigacion micrologica de la estructura del pelo en los
Monotremas.
Lo mismo Ornithorhynchus que Tachyglossus poseen varios tipos diferentes de pelo en su cuerpo. El tipo de pelo que parece ser caracteristico de los Monotremas es el de tipo muy aplanado, representado por los pelos denominados pelos escuteliformes en Ornithorhynchus y por los pelos Uamados pelos ondulosos aplanados y pelos espinosos en Tachyglossus. Ornithorhynchus posee un recubrimiento de pelos semej antes a los que forman la piel de otros mamiferos, los cuales faltan en Tachyglossus. La estructura de dichos pelos es semej ante a la del tipo general de pelos cilindricos que se encuentran en la mayor parte de los mamiferos.
Translation by Jos6 F. Nonidez Cornell Medical College, New York
AUTHOR S ABSTRACT OP THIS PAPER ISSUED BY THE BIBLIOGRAPHIC SERVICE, JULY 12
A MICROLOGICAL INVESTIGATION OF THE HAIR STRUCTURE OF THE MONOTREMATA
LEON AUGUSTUS HAUSMAN Zoological Laboratory, Cornell University
FOUR PLATES (nINETY-EIGHT FIGURES) AND THREE TEXT FIGURES
CONTENTS
Introduction 463
Collection of hair samples 463
Preparation of hairs for microscopical examination 464
The hair of OrnitJiorhynGhus anatinus 472
Summary for Ornithorhynchus 479
The hair and spines of Tachyglossus hystrix 479
Summary for Tachyglossus : 484
Bibliography 485
INTRODUCTION
The observations and conclusions embodied in the present contribution are the outgrowth of a comparative study of the microscopic structure of the hairs of the monotremes, Ornithorhynchus anatinus and Tachyglossus hystrix, and incidentally and for comparison of members of all of the existing families of mammals, except the Cetacea.
Collection of hair samples
The majority of the hair samples were collected by the writer from skins and mounted specimens in the collections at Cornell University and from those in the American Museum of Natural History in New York City and in the United States National Museum in "Washington. Other institutions kindly furnished many samples.
Within each family samples were examined from species representing various types of environments, and from each family
463
464 LEON AUGUSTUS HAUSMAN
three species were selected, where possible, to illustrate the typical trichologic structures in their various modifications.
It was found that, after collection, the hair samples were most satisfactorily disposed of by placing them, together with their data slips, in gelatin veterinary capsules. One-ounce capsules were used for the longer hairs, and half- and quarter-ounce for the shorter ones. These containers were much more satisfactory than glass vials, for they could be transported loosely, with little care, without danger of breakage; were less expensive, and much lighter in weight.
Preparation of hairs for microscopical examination
1. Preparation for examination of cuticular scales. First method — dry mounting. Some authors recommend placing the hair directly beneath the microscope on a slide and making the examination dry, without previous preparation. This method was tried, and while it revealed in general the arrangement of the scales in those hairs which are coarse and in which the scales are unusually prominent, it failed to yield accurate results. It was found to be quite essential to have the hair shaft perfectly clean, otherwise dust fibers which adhered to it were quite likely to be mistaken for the fine transverse markings which indicate the outlines of the scale edges. The simplest method of preparation employed was that of washing the hair carefully in a solution composed of equal parts of 95 per cent alcohol and ether. This removed all the oleaginous matter from the surface of the hair shaft and made it difficult for dust fibers to find lodgment upon it. It was then transferred to a clean slide, covered with a cover-glass, and allowed to stand on a tripod over a low alcohol flame until the whole had become perfectly dry. Throughout the entire manipulation of hairs it was found to be absolutely imperative to keep all utensils and instruments, and especially all glassware, scrupulously clean. A dry examination of the hair was then made. This sort of treatment was found to be effective in the examination of hair whose scales were large or prominent, such as the hair of some of the Cervidae, or of the Camelidae. In the great majority of cases, however, it became necessary to have
HAIR STRUCTURE OF THE MONOTREMATA 465
recourse to some methods of staining or of otherwise rendering the scales more certainly visible.
Second method — thickening the cuticular scales. Several methods of rendering the cuticular scales visible by treating the hair with reagents which thicken the scales, making them stand out from the cortex, are sometimes used. In the writer's opinion, such methods cannot to advantage be employed where a careful determination of the exact scale form is the end in view. By a series of experiments he has become convinced that the use of caustic potash or soda, sulphuric acid, and so forth, which are recommended for use, often hot, distort the scales, and furthermore cause them to bulge and to project outward from the cortex in an unnatural manner. This destroys at once both their characteristic outlines and their relationships one with another. Cuticular scales which have thus been dissociated from the cortex may, by pressure upon and a gentle rotation or agitation of the cover-glass, be entirely loosened from their connection with the remainder of the hair. Such scales are believed not to be useful for a careful correlative study of form. It was found that the following procedures might be used in the maceration of hairs for the dissociation of the cuticular scales where merely a crude notion of their form was the goal desired. Such scales revealed, in a general way, the arrangement patterns in which they were disposed about the hair shaft. These methods are: 1) heat gently in a 10 per cent aqueous solution of acetic acid until the hair shaft is slightly softened; 2) treat similarly, using a 1 per cent aqueous solution of chromic acid; 3) boil in a 5 per cent aqueous solution of hydrochloric acid. In each case various trials are necessary before the requisite degree of softness of the hair shaft can be obtained. After any of these procedures, the hairs may be mounted in water before examination, in order that the scales may float outward and not cling tightly against the cortex.
Third method — staining. The method which afforded the greatest measure of success, however, was one which was devised after the method of thickening the scales, and thereby distorting them, with caustics or acids, had been tried. The external sur
466 LEON AUGUSTUS HAUSMAN
face of the hair shaft presents an alternating series of transverse ridges and transverse depressions, due to the overlapping, imbricate cuticular scales. The method devised for making clear the outline of the scales is, in principle, to lodge finely divided coloring matter in all of these transverse depressions, leaving the elevations uncolored. This was accomplished in the following manner: The hair shaft was first washed in a solution composed of equal parts of 95 per cent alcohol and ether, to free its surface from oily matter. It was then heated very slightly or fanned gently, to insure complete drying, and then immersed in a 95 per cent alcoholic solution of gentian violet or safranin. After remaining in this solution for a minute or more, it was removed with forceps and held in a gentle draft of air or in the current of warm air rising from a bunsen flame until the alcohol had completely evaporated. The gentian violet or safranin, it was found, had been deposited from the solution and had gathered in all the transverse depressions on the surface of the hair, thus marking out clearly the outline, in sharp color, of every cuticular scale. The most delicate scale sculpturings which are capable of determination upon the finest of the hairs with the immersion objectives were by this method of treatment rendered plain, though for the very finest of the hairs this method was combined with examination under oblique illumination, hereafter described. It was found, however, that while this method gave almost ideal results with some hairs at the very first trial, it was necessary with other hairs to subject them to the processes again and again before the evaporation of the alcohol deposited the pigment uniformly in the cuticular grooves over any considerable portion of the hair surface.
Other stains which go easily into solution in the 95 per cent alcohol and are readily deposited upon its evaporation, such as iodine (with potassium iodide), methyl green, methyl and methylene blue, and toluidin blue, were also used, but for some unknown reason the best success was obtained with the gentian violet and safranin.
In the case of those hairs in which the scales are so prominent as to project notably out from the shaft, a very striking profile
HAIR STRUCTURE OF THE MONOTREMATA 467
was obtained by soaking the whole hair (after washing in the ether-alcohol solution) for several minutes in a 10 per cent aqueous solution of caustic soda, yet not long enough to render the hair slimy or to distort the scales, and then dipping it into a pink solution of safranin and 82 per cent alcohol. The entire surface of the hair assumed a pink color, and while the scale sculpturings over the surface of the hair were obliterated by the uniformity of the coloration, yet the profile of the hair shaft stood out with great clarity against the white light of the microscopic field, or even more strikingly against the black background when very oblique illumination and a low-power objective were utilized. This manipulation was often resorted to to determine the relation of the transverse scale sculpturings on the surface of the hair to the profile of the serrate edge.
Figure A
For immediate examination the hairs stained to show the scale sculpturings on the surface were put into temporary dry mounts by fastening over them a cover-glass touched about its edges with balsam. Permanent mounts were obtained by ringing the coverglasses with cement upon a turn-table. They were often, for immediate use, also mounted in very viscous gelatin gum dammar, or balsam. It was found that if very fluid balsam, dammar, or gelatin were used, the coloring material was quickly dissolved from out the scale depressions and distributed throughout the whole of the mounting medium. For the coarser hairs dry mounts were the most successful; for the finer, the glycerin, balsam, and dammar mounts.
It was frequently found desirable to trace completely around the hair the course of the markings indicating the edges of the cuticular scales, particularly in the study of the form of the coronal type of scales. To render the rotation of the hair under the highest powers of the microscope practicable, the apparatus shown in figure A was devised, and termed 'hair rotator.' It was con
468 LEON AUGUSTUS HAUSMAN
structed as follows: Upon a glass slide were fastened with Canada balsam two small corks, of firm texture, transpierced by fine copper wires, with their opposite ends bent into loops. Between the inner loops of these wires and between the corks, the hair under study was stretched and fastened at each end with droplets of balsam or viscous mucilage. The copper wires were now drawn out carefully away from one another until the hair between them was stretched taut, and the whole device placed upon the stage of the microscope. By gently tapping the outer loops of the copper wires with a dissecting needle, the hair could be with the greatest delicacy turned in either direction while under examination. It was discovered that a small drop of a 25 per cent aqueous solution of caustic soda or potash placed near one extremit}^ of the stretched hair softened this portion to such an extent that the hair could be more easily rotated by turning but one of the copper wire loops. Not only could the hair be rotated, but also stretched slightly, and this was an advantage often, inasmuch as the lengthening of the cortex slightly separated the cuticular scales and rendered the depressions between them a trifle deeper. This device proved equally useful also in the examination of the medulla. The hair was first washed in the ordinary way, as has been described, and then cleared in clove or cedar oil, after which it was dried between two pieces of lens paper and stretched in the hair rotator as previously described. The configuration of the medullary cells and the relation of individual and groups of cells to each other was by this means brought out in the most satisfactory manner. Several of the hairs were, after having been cleared in xylene, allowed to remain in a bath of balsam for several hours, and then taken out, hung up like candles, and allowed to dry covered with a thin film of hardening balsam. These were then mounted in the hair rotator, and thus a completely balsam-mounted hair secured for examination. It was found, however, that in the main this precedure gave no more satisfactory results than simply clearing in clove or cedar oil before mounting in the rotator, though there were instances in the cases of some of the larger hairs in which it was thought that the clearing in xylene insured a slightly greater clarification of
HAIR STRUCTURE OF THE MONOTREMATA 469
the hair shaft. For the study of both, the cuticular scales and the medulla with the hair rotator, both reflected and transmitted light were employed. Were the device made in such a way that the hair was held more closely to the upper surface of the slide, no doubt both indirect (or dark-field illumination) and polarized light might also be utilized with advantage. For securing a profile view of the hair, with its serrated outline of the cuticular scales, the rotator was used with reflected light, the source of which was placed in front, slightly above and a little to the side of the microscope, and the slide beneath the hair covered with black unglazed paper.
Another method of securing a profile view of the hair was to use indirect lighting or dark-field illumination, with the hair mounted dry. This method of illumination was best secured by the use of the dark-field illuminator, in which the central column of light is intercepted by an opaque disc in the condensing lens. For all dark-ground work it was found necessary to utilize a very brilliant light, especially with the higher powers. Because of the great degree of obliquity of the light required when using the 1.8-mm. (or higher) objective, it was necessary to form an oil connection between the upper surface of the condensing lens and the lowef surface of the slide. If this is not done, nearly all of the light passing through the condenser from the mirror will not be transmitted through the upper surface of the former, but will be reflected, leaving the object to be examined in darkness. The use of oblique light was found necessary in many cases to demonstrate to the examiner's satisfaction the relations of the finer markings on the surface of many of the smallest hairs — markings that proved to be elusive under any of the methods of treatment heretofore described.
In the study of the medulla the dark-field type of lighting was also found helpful, though here the grosser structure of this element of the hair shaft rendered such refined manipulation not so essential.
In certain instances the polariscope was found to be an invaluable aid, particularly in detecting the presence within the hair shaft of vestiges of meduUary cells or groups of cells, and in indi
470 LEON AUGUSTUS HAUSMAN
eating the extent of sonie of the cuticular scales. The disposition of the colors shown indicated often the location and relative thickness of the various hair elements, and not infrequently caused the transverse edges of the cuticular scales to stand out prominently in black tracery against the background of some vividly contrasting color. The state of fusion of the cortical cells was often also indicated by the appearance of certain characteristic color associations. By arranging the hairs under examination at different angles on the slide and by including in one mount hairs of many different species, various beautifully colored demonstrations of differences and similarities were obtained. It was found most satisfactory to mount hairs designed for polariscopic examination in some heavy oil (e.g., castor oil) or balsam. This treatment was, in fact, imperative for those hairs whose medullas were the objects of investigation.
2. Preparation for the examination of the inedulla. The methods used to render the scales of hair prominent obscure the medulla. Consequently it was found necessary to devise some means of rendering the hair shaft transparent in order to bring the medullary cells or chambers into visibility. This was accomplished in the following ways :
First method — clearing in water. This is the method of clarification commonly used for hairs of a not too great diameter in general. It works fairly well with the finer hairs which lack pigment in the cortex and whose cuticular scales are not closely set together, which is tantamount to saying that it works well with but very few.
Second method — clearing in oils. It was found that clearing the hair in oils of various sorts, such as oil of bergamot, oil of cloves, oil of cedar, oil of origanum, and castor oil, tended to obscure almost entirely the markings of the scales and to make the hair shaft, in effect, a glassy cylinder, through which the medullary cells could be seen with great distinctness. The hair was first washed in the ether-alcohol solution as before, and then transferred to a bath of oil, where it was allowed to remain for several minutes. It was then mounted in the same oil for microscopical examination. In the case of the larger hairs, it was often neces
HAIR STRUCTURE OF THE MONOTREMATA 471
sary to transfer the hair from the ether-alcohol solution to 95 per cent alcohol, then to a solution composed of equal parts of 95 per cent alcohol and the mounting oil, and then to the mounting oil itself. In each of these solutions the hair was allowed to remain for several minutes before transferring it to the mounting oil. The latter was often heated to 100°C. or thereabouts, to insure its penetration into all of the transverse ridges of the cuticular scales.
Third method — clearing in balsam. Often the finer hairs were cleared and mounted in balsam. After having been washed in the ether-alcohol solution, they were dried and immersed in a bath of xylene and then transferred directly to a mount of very thin balsam. With hairs as those of the bats, shrews, and many of the rodents, this treatment proved to be the best.
3. Sectioning and inounting. Transverse and longitudinal sections of the larger spines, such as those of the spiny ant-eater {Tachyglossus hystrix) (figs. 52 to 56), were secured by fastening the spine between two pieces of very hard, firm-grained cork in an immovable fashion, and then filing the spine to the desired thinness with a smooth, parallel-grooved file. The section was then removed from the cork and ground gently upon a hone moistened with water to render the surface perfectly smooth, after which it was dehydrated in several alcohols, impregnated with xylene and xylene-balsam, and mounted in balsam in the usual way. Those possessing the pithy type of medulla were differentially stained with eosin, the medulla taking the color, the firmer cortex and cuticle not.
For hairs in general the usual processes of dehydrating, impregnating with xylene, paraffin-xylene, infiltration with paraffin, mounting on blocks, sectioning, staining, and mounting were employed. It was found advisable to use xylene and paraffinxylene baths hot, and to keep them so in the oven, allowing the hairs to remain therein for several days each. In staining with eosin, safranin, gentian violet, or methyl green, the medulla always took the stain, the cortex and cuticle remaining uncolored.
With most hairs, and more particularly with the finer ones, a very hard paraffin gave the best results. When it occurred that
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, NO. 4
472 LEON AUGUSTUS HAUSMAN
the hairs pulled from out the block during the sectioning, a longer period in the hot xylene and zjdene-paraffin baths was found to be the remedy.
The author here wishes gratefully to acknowledge his indebtedness to the Museum of Vertebrate Zoology of the University of California and to the Peabody Museum of Yale University for hah' samples sent him, and to Dr. G. S. Miller, of the United States National Museum at Washington, and Dr. J. A. Allen, of the American Museum of Natural History in New York City, both for sending hair samples and aids of one kind and another at various times, and for allowing the author the free use of their extensive collections of skins. Dr. A. H. Wright, of the Department of Zoology at Cornell University, lent his kindly aid in the determination of some of the vernacular names of species mentioned in this paper.
Especial thanks are due to Professor H. D. Reed and to Professor Simon Henry Gage for guidance and counsel during the course of the investigation.
THE HAIR OF ORNITHORHYNCHUS ANATINUS
The hair types of Ornithorhynchus (plates 1 and 2)
The fact that Ornithorhynchus possesses two distinct types of hair was made known in 1802, when Blumenbach (1802) described its gross appearance. Later Home (1802) recorded the same facts. Apparently independently, Glockner (1819), van de Hoeven ('23), and Peron and Lesseur ('23) made a more careful study of some of the structural features, in a general way. A summary of the observations up to the year 1825 was made by Meckel ('26). The relations of the hairs to each other within the follicle was the subject of the investigations of Leydig ('58) while the size and general gross appearance of the hairs occupied the researches of Welcker ('66).
The first systematic attempt to review the histology of the hair is that of Waldeyer ('84), who was followed in this same endeavor by Poulton ('94). The latter first clearlj^ indicated the relation
HAIR STRUCTURE OF THE MONOTREMATA 473
ship between the flattened hair and the fur hair. He applied the term 'shield' to the tips of the flattened hair, which suggested to the present writer the term 'shield hair/ which is here employed as a designation of the larger hairs, to distinguish them as a group from the finer, or fur hairs, in which the shield does not appear.
Spencer and Sweet ('98-'99) declared it their belief that in structure and in growth, the hairs of the Monotremata are not different from the hairs of the members of the higher orders, while on the contrary, Toldt ('05) maintained that hairs with thickened ends (the shield hairs), such as Ornithorhynchus possesses, is to be found nowhere else among mammals. This statement he retracted a year later, however, when he discovered that the hairs of Tachyglossiis were structurally the same.
Upon the body of Ornithorhynchus are six rather well-defined areas, each bearing its characteristic type of the longer protective shield hair. The type covering the greater part of the body is that found upon the dorsum (fig. 1, F). This type occurs over the whole of the back, caudad of the area of truncated shield hair (fig. 1, C), and is regarded as the form which all of the protective hairs of the body would assume, were not some worn off at the tips during growth.
Figure 3 shows the characteric form of the dorsal shield hair, and figures 13 to 31 its structure. The shield hairs upon the other parts of the body exhibit similar structural details, but each type possesses its own distinctive distribution of pigment. Of this distribution later mention will be made.
The tract which is here called the area of truncated pigmented shield hair (fig. 1, C), bears hair possessing shields whose truncated tips indicated that they are exposed to considerable attrition. These hairs, and more particularly those between the eyes, contain less pigment than the dorsal shield hairs, varying from a light to a distinctly yellowish brown. Upon the pinnae of the ears and likewise over a small area immediately surrounding them, the shield hair is lacking altogether, and its place is taken by a very fine, short, soft fur hair, a continuation of that occurring beneath the shield hair over the larger portion of the body. This fur hair of the pinnae is the finest which the animal possesses.
474 LEON AUGUSTUS HAUSMAN
Covering the venter is a type of the shield hair somewhat similar to that which clothes the head, but bearing a much longer shield, and, as might be expected, containing less pigment (fig. I, D). Upon the sides of the venter (the region of the transition in color from the dark brow^n of the back to the creamy white of the abdomen) the pigment is confined to the proximal fourth of the shield. In all cases the shaft of this venter hair contains so few of the brown pigment granules as to show no color except under the microscope.
From the middle of the back to the base of the tail the shield undergoes a progressive increase in length and rigidity, and the shaft becomes correspondingly shorter (fig. 5). When the tail is reached each hair consists almost wholly of the flattened, stiffened shield element, a construction which gives it the character of very fine bristles. Near the base of the tail the top of the shield is weakly pigmented, while near the end of the tail the shields of the hairs exhibit an increased number of pigment granules.
The tail hairs are similar to those of the feet, and are subject to much attrition. They are consequently considerably worn and frayed, and are held closely against the skin. The forefeet are almost entirely shorn of their hair as far as the wrist, since it is upon these feet that the brunt of the labor of swimming and of burrowing falls. Upon the hind feet more hair is present. On both feet the hair is of a light brown color. Unlike the shields of the hair upon the venter, the shields of the hair of the feet are pigmented with their characteristic color throughout their lengths. This suggests that the lighter color of the hair upon the fore feet is not due to the fact that the tips of the shields have been worn away.
In all these varieties of the shield hair the three elements, shield, isthmus, and shaft, are invariably present (fig. 14, B, C, D), though different elements rise into prominence and determine the gross appearance of the hair upon different parts of the body (figs. 3 to 7). In all of these vari-eties, likewise, the relationships between the cortex, medulla, and cuticle are fundamentall the same, but in certain of the hairs, as will be shown, the medulla is lacking altogether.
HAIR STRUCTURE OF THE MONOTREMATA 475
There exists a variety of the shield hair ^^hich differs so markedly in its appearance from all the other types as to suggest at first the necessity of according it a separate classification. This aberrant type is restricted to a meager tract about the base of the snout, more particularly to an area just ventrad of the base, a region which may be termed the chin (fig. 1, ^). Figure 8 shows the gross appearance of this hair, and figures 32 to 35 its structure. All distinctions between shield, isthmus, and shaft have disappeared, but the configuration of the cuticular scales, their mode of imbrication, and the character of those dissipated medullarycells which still remain are the same as those of all the other types of shield hairs. The fact that these ultimate structural elements of the hair preserve their integrity of appearance even though the general aspect of the hair as a whole may be radically modified, would seem to substantiate the assumption that, in Ornithorhynchus at least, the cuticular scales and the medullary cells offer the readiest means of identification and the most trustworthy criterion for the classification of the various types of hair.
The finer hair, found next the skin and underneath the shield hair, and which will be termed the 'fur hair,' is of a grayishbrown color, a trifle darker on the dorsum than on the venter. It covers the entire bodj^, with the exception of the tail and feet, and is everywhere approximately from one-third to one-half the length of the shield hair (fig. 9). Vestiges of this fur hair may sometimes be found upon the tail in adults and a considerable amount is present on the tail of young individuals. This fur hair soon disappears, as a rule, early in adult life over such portions of the body as the tail and more distal portions of the limbs, where its presence is unnecessary for warmth and protection from water. Like the shield hair, the fur hair occurs upon one restricted portion of the body in a much modified form, namely, upon the area immediately surrounding the pinnae of the ears. Here it differs from the typical form in both length and diameter, though its characteristic histological structures are unchanged. It is, as has been said, the softest and finest hair which the creature possesses.
476 LEON AUGUSTUS HAUSMAN
The medulla of the fur hair is somewhat similar to that of the shield hair (fig. 42), its principal differences lying in the conformation of the individual cells and in their closer compaction in the shaft. The shield hair, however, possesses a structurally distinctly different medulla in the region of the shield (figs. 23, 24, and 42).
The hairless areas of the body are the ventral surface of the tail and the distal portions of the fe6t. The denuded state of the former is acquired by the wearing away of the few hairs which make their appearance in the young. Stumps of these early hairs remain imbedded in the follicles throughout the life of the animal and apparently continue to grow, but are constantly worn away. A similar condition obtains on the distal portions of the feet.
The cuticular scales of the shield hair. At the base of the shield hair shaft the exposed portion of the cuticular scales is triangular in form, with the acute apex directed distad (fig. 15). As the middle of the shaft is approached, the scales become more obtuse, until their edges form a series of fine, transverse, roughly parallel ridges extending obliquely across the shaft (fig. 13). No difference in the thickness of the cuticle of the extal and ental surfaces of the cylindrical shaft are apparent (fig. 20) .
The scales of the isthmus (fig. 14, C) , are like those of the shaft in outline, but are smaller and more compactly grouped. The transverse markings indicating their edges are, in consequence, more crowded. Due to the angle at which the isthmus is bent, the scales in the convex region of the bend are much more closely impacted than those above and often present the appearance of having been fused into a solid plate. This is due to the fact that, the edges are so closely crowded together that they are not distinguishable except under very careful examination. Upon the outer, or convex side of the bend, where the wear occurs, the scale edges are much modified in outline and present a much more evenly parallel appearance than any of the others. From this and from similar observations on other hairs in various situations upon the bodies both of Oniithorhynchus and of other species of mammals, it is concluded that the change in form be
HAIR STRUCTURE OF THE MONOTREMATA 477
tween the scales of the proximal and the distal portions of hairs is due to increasing amounts of attrition and consequent removal of material from the free distal edges of the scales. On the shield itself their edges are also much worn and smooth (fig. 14). This condition is best illustrated in the shields of the hairs from the tail and feet (figs. 5 and 6). Scales from different regions of the shield hair are shown in figures 13 to 17.
The distinguishing feature of the cuticle of the shield is, however, its greater thickness on the ectal than on the ental surface, the difference being due, possibly, to a demand for maximum protection where maximum attrition occurs (fig. 19).
The medulla of the shield hair. The medulla of the shaft, in its characteristic appearance, is shown in figure 13. Toward the base of the shaft (fig. 12, Q) it pinches out, existing only as isolated, elongated cells. This it also does at the isthmus, but reappears again faintly in the base of the shield (fig. 14). About two-thirds of the way toward its tip it gathers together again in a well-defined band, but with a different structure from that which it possessed in the shaft (fig. 17). The region of this reappearance of the medulla in the shield is not always the same in different hairs; sometimes it is found nearer the tip, sometimes nearer the middle. The relation of the medulla to the cortex in the shield and shaft is shown in figures 13 to 18.
Upon a gross examination the medulla of the shield appears similar to that of the shaft, but a minuter study reveals the fact that the two differ markedly in their cellular elements. In the former the cells are globular, of various sizes, and are grouped into botryoidal masses; in the latter they exist as discoid cells, of uniform size and shape, and are regularly superimposed (figs. 23 and 24).
The shield hairs of the feet and tail, which apparently consist almost \\'holly of the shield element, bear medullas which do not at all resemble those of the shields of the back just described. Although the cells are somewhat fragmentary, they resemble those of the shaft of the shield hair (figs. 26 and 27). Cro: ssections of these hairs show that the cuticle is no thicker on the extal than on the ental surface. Here likewise they resemble the
478 LEON AUGUSTUS HAUSMAN
shaft of the tj'pical shield hair rather than the shield. It may be that these hairs represent, anatomically, an expanded and flattened portion of the shaft element rather than an added shield element. The name shield hairs, however, in this case is not a misnomer when taken to refer to the form of the hair and not to its derivation.
The cortex of the shield hair. The cortical element is that to which is primaril}^ due the variations in form of the shield hair. In its simplest condition in the shaft of the hair it consists of elongated, distorted, fused, nucleated cells, which are compacted longitudinally as shown in figure 22. In the shield the cortex expands and comprises the major portion of that structure (figs. 17 and 19). It is this element of the hair structure also which bears the pigment to which the color of the hair is due. In all but the cortex of the shield this pigment is distributed uniformly, but here it occurs most abundantly in the form of masses of granules in the ectal half of the shield (fig. 19).
The relation of the cortex to the medulla and cuticle in the shield hairs of the feet and tail is shown in figures 25 to 29.
The cuticular scales of the fur hair. The cuticular scales of the fur hair also differ in form from the base to the tip of the hair. Near the base the scales are very elongate (figs. 38 and 39) and their free distal edges project away from the shaft, giving to it a distinctly serrate profile (fig. 38) .
Near the middle of the hair the worn edges of the scales give the hair the appearance shown in figure 42, and near the tip that illustrated in figure 37.
The mediiUa of the fur hair. No marked difference between the medulla of this type of hair and that of the shaft of the shield hair exists. Throughout four-fifths of the length of the shaft the medulla persists (fig. 42), and near the tip, where it does gradually' thin out and disappear, there is no place where it shows any modification in form such as that which is noted in the case of the shield of the shield hair of the dorsum.
The cortex of the fur hair. This element presents no differences from its homologous structure in the shaft of the shield hair.
HAIR STRUCTURE OF THE MONOTREMATA 479
Summary for Ornithorhynchus
Ornithorhy nch us anatinus possesses six well-defined areas upon the body, each of which is characterized by the growth of a different kind of hair. These different kinds, or varieties, have, apparently, judging from the form of the cuticular scales and medulla, been derived from two structural!}' distinct types of hair, the fur hair and the shield hair.
The shield hair, because of its structure, acts as a protection against physical injury to the skin and precludes the entrance of water, while the fur hair serves as an insulating medium, guarding the body against changes in temperature.
THE HAIR AND SPINES OF TACHYGLOSSUS (ECHIDNA) HYSTRIX The hair and spine types of Tachyglossus (plates 3 and 4)
The first systematic account of the body covering of Tachyglossus was given by Meijere in 1894, and in 1898 an account virtually similar, but with especial consideration to the disposal of the groups of hairs and spines, was published by Romer. During 1898 also, Spencer and Sweet had issued their work on the development of the hairs and spines in the monotremes and marsupials, in which a careful study is made particularly of the development of the new hairs and spines and of the various follicular layers taking part in their growth.
Toldt ('05), in a discussion of the genera which he maintained as Proechidna and Tachyglossus, was the first to suggest that the criterion of hair structure and form is, at least as far as these genera are concerned, significant from the standpoint of their phylogenetic stud}^, and may be used as aids in determining the position of the species. In 1906 he described the hair and spine covering of a species allied closely to the one now under consideration, Zaglossus hruijjnii hruijjnii.
A further contribution to the knowledge of the growth and development of the hairs and spines, with especial emphasis upon their grouping in the skin, was made by Pinkus injl906.
The body covering of Tachyglossus has been commonly described as of two types, spines and hairs. This is, however, a
480 LEON AUGUSTUS HAUSMAN
very general classification and may be used only in a rough way to indicate the general nature of the centering of the dorsum and venter, respectively. The covering of the latter consists of long, stiff hairs, while the former is beset with long, sharp, rigid spines so thickly placed as to cover effectively both the skin and their own bases.
A closer examination of these spines and hairs reveals the fact that no definite line of demarcation can be drawn between them. From the longest and most robust of the spines of the back to the finest of the hairs which can be found on the venter, there exist all gradational estates. More will be said later regarding this transition in form from the hairs to the spines. It ^^ill first be necessarj^ however, to pass in review the various parts of the body with reference to the type of hair and spine covering which each possesses.
The dorsum (fig. 43, G) is, as has been said, clothed with a formidable panoply of long, rigid, acuminate spines, closely massed together. The largest of these are those which occur in what we shall term the 'hip tufts' (fig. 43, F). These spines are approximately 50 mm. in length and about 4 nmi. in diameter in their thickest portions. They are of a light yellowish-white hue with very dark brown, almost black, tips, the color extending down the spine for a distance of about 7 mm. in the case of the longest spines (fig. 54). The smaller dorsal spines are like the larger, with the exception that their tips are pigmented for a greater distance down the shaft, often extending to one-fourth its entire length (fig. 56), Because of the closeness with which the larger spines are set together, the lower three-fourths of the shafts of the smaller spines are hidden. Thus it appears as though the dorsum possesses spines of two colors, large yellowish spines and smaller black ones.
The hair of the dorsum is obscured by the spines, and consists of two general types : one flattened, straight, and somewhat stiff and spinous (fig. 58), and the other smaller, also flattened and somewhat stiff, but, in addition, slightly wavy (fig. 59).
Upon the venter occur three types of hair: a spiny, flattened type (fig. 48), a flattened wavy type (fig. 47), and a still finer
HAIR STRUCTURE OF THE MONOTREMATA 481
flattened and more wavy type (fig. 45). The first two are similar to the spiny and wavy hairs already described as occurring on the dorsum.
The covering of the tail is similar to that of the dorsum except that the spines are a trifle more slender and acuminate (figs. 60 and 61). About the periphery of this caudal tuft of spines occurs a zone or border of smaller spines which are unpigmented, and are much lighter in color than any of the spines elsewhere upon the body. Whenever the spines of the tail are elevated, these lighter marginal spines obscure the darker ones in the center of the tuft and cause the tail to appear a light creamy white color, and consequently to be very conspicuous when viewed from behind.
Upon the head occur short, light colored spines (fig. 62), short spiny flattened hairs (figs. 63 to 65), and short wavy hairs (fig. 66). All of these are similar to the spines and hairs of the dorsum, but shorter.
The flanks are covered by small curved spines (fig. 50) and long spiny hairs (fig. 49) which appear to be transitional between the spiny hairs of the venter and the curved spines of the flanks just mentioned.
The feet bear long spiny flattened hairs and shorter flattened wavy hairs as does the venter, though these of the latter type are few in number or absent altogether.
A comparison of figures 45 to 53 will give a notion of the nature of the transition from the finest wavy hair of the body to the most robust of the spines which are found in the hip tufts.
The wavy hair with its thickness slightly increased becomes the flattened straighter type shoAvn in figures 47 and 48, and this becoming still thicker, especially in its medial portion, gives rise to the spines of the type illustrated by figure 50. A progressive increase in length and thickness of such a spine produces those of the types represented by figures 51 to 53, successively.
Thus a comparison of the gross characteristics of the hairs and spines suggests a transition in form, and an examination of their microscopic structure lends support to such a supposition.
482 LEON AUGUSTUS HAUSMAN
The cuticular scales of the hairs and spines. The finest of the hairs — the wavy hairs from the auricular depression (fig. 43, A and E), dorsum (fig. 43, G), and venter (fig. 43, 7) — bear the largest cuticular scales (fig. 87), and as we pass in our examination from the wavy hair to the thicker, stiffer, straighter type (the type here called the flattened spiny hair), we find that the scales decrease in size; their edges become more closely set together. The greater the thickness of the spiny flattened hair (and the consequently greater spinosity), the smaller, relatively, and the more irregular in ectal outline are the cuticular scales.
This alteration in the form of the scales is illustrated by the three types of the spiny flattened hair, each one, in the order given, being thicker and consequently a trifle more stiff and spinous than its predecessor. These types are : the spiny flattened hair of the dorsum (fig. 58) , the short spiny flattened hair of the top of the head (fig. 64), and the long spiny flattened hair of the venter (fig. 67). A comparison of the figures referred to will make clear the relations of the scales. It will be noted that the larger and stiffer and more spinous the hair becomes, the smaller, relatively, are the cuticular scales and the more closely are their ectal edges crowded together.
As the transition from the spiny hairs to the true spines progresses, so also does the decrease in the relative sizes and irregularity of the scales, until upon the surface of the true spines, such as the largest of those found upon the dorsum, the scales are so closely massed together as to render the tracing of their individual edges extremely dilEcult. Ihese can be seen only near the base of the spine; higher up the attrition, to which so stiff an appendage as a rigid, immobile spine is subjected, leaving the surface smoothly polished and obliterating all traces of the edges of the scales.
The mednlla of the hairs and spines. The medulla likewise shows regular transitional forms between the wavy hairs and the spines. In the fine wavy hairs it is to l^e found only as streaks of minute, isolated cell fragments in vaiious portions of the hair shaft, which, as has been indicated in the discussion of the hairs of the mammals in general, may denote that this type of
HAIR STRUCTURE OF THE MONOTREMATA 483
hair has been derived from a still finer variety which possessed a complete medulla. These isolated medullary cell fragments in the shaft are never in a continuous band. Seldom, indeed, are they discoverable. Often a close search of the entire length of the hair shaft with the highest powers of the microscope is necessary before the minute vestiges of the medulla can be described. They are, I think, present in some degree in all wavy hairs (figs. 85 and 86).
In the spiny flattened hairs more of the medulla appears, although it still exists, in most instances, as streaks of isolated cell fragments (fig. 89). At the base of the shaft, in this type of hair, and just below the mouth of the follicle, there often occurs a large group of medullary cells which resembles the fully formed medulla found throughout the shaft of the smaller spines. This group of cells pinches out and disappears just before the emergence of the hair shaft from the mouth of -the follicle (fig. 80). Waldeyer observes that in the center of the large, strong spiny hair there may occasionally occur large, nodose, pigment masses (as he calls them) which perhaps may be regarded as the rudiments of a medulla. That these masses are medullary cells, I think there is now no doubt.
At the ectal extremity of the spin}^ flattened hair of the dorsum there commonly occurs, for the first time in the series, a complete medulla (figs. 71 and 72) which persists for a short distance down the shaft and then fragments into minute particles as the middle of the hair is approached (fig. 73). These fragments become progressively smaller and fewer in number in the lower portion of the hair (fig. 74), but gather together again into a continuous medulla at its base (fig. 75).
In the smaller spines the medulla is complete, and in the larger it reaches its maximum expansion, occupying an important position in the structure of the spine (figs. 94, 95, 96, and 98).
The cortex of the hairs and spines. The cortex in all the hairs and spines is a homogeneous hyaline, horny mass, in which no distinct evidences of its fused component cells could with certainty be determined. \^Tien macerated in a 25 per cent aqueous solution of sodium hydroxide it splits up into a fibrous mass,
484 LEON AUGUSTUS HAUSMAN
which may be suggestive of the configuration of the fused cells. Similarl}^ when a spine is broken obliquelj^ across, the irregularity of the fracture of the broken cortex element may also be indicative of the original cell form (fig. 98, B.CO.), though it may be that these cortical cells have lost all originality of contour and have completely fused into a truly homogeneous substance. At present no statement can be made regarding their form in the various hairs and spines.
While it is not within the province of this paper to discuss the development of the hairs and spines, from what has been observed it may not be amiss to call attention to the supposition that the different varieties of hairs and spines of Tachyglossus may have been derived from a single hair type, possibly of the wavy variety, by an increase in the thickness of the middle portion of the shaft. Their development can be determined with certainty, however, only by a careful study of the stages of their growth from the follicle in the embryo and young.
Summary for Tachyglossus
In all essential respects the hairs of Ornithorhynchus and Tachyglossus are similar. The curious flattened type of hairs is the characteristic form for this order. In both Ornithorhynchus and Tachyglossus this type comprises about 50 per cent of the body covering. In Tachyglossus the suggestion is advanced that the spines are developed from the wavy hairs. Not only in structure, but also in development are the hairs of Ornithorhynchus and Tachyglossus alike. Spencer and Sweet observe, So far as essential points are concerned, the development of the large and small hairs alike agrees in both Ornithorhynchus and Echidna [Tachyglossus\J'
The type of hair, therefore, characteristic of the IMonotremata, is the flattened type, represented by the shield hairs of Ornithorhynchus and by the flattened wavy and spiny hairs of Tachyglossus. On the other hand, the fur hairs, found in Ornithorhynchus, but not present in Tachyglossus, are like the general type of cylindrical fur hairs possessed by the majority of the mam
HAIR STRUCTURE OF THE MONOTREMATA 485
malia. Text figures B and C, representing the structure of the fur hairs of the European mole {Talpa europaea) and the^ pygmy flying phalanger (Acrohates pygmaea), respectively, illustrate this similarity.
Figure B Figure C
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Beddard, F. E. 1902 Observation on the carpal vibrisse in mammals. Proc.
Zool. See, Lond., p. 127. Blumenbach 1802 Anatomical observations on the structure of Ornithorhtjn chus paradoxus. Phil. Mag., vol. 11, p. 366. BoHM, A. A., AND Davidoff, M. von 1900 A textbook of histology. Bosch, E. 1910 Untersuchungen ueber die Ursache der Haarwirbrldung bei
den Haustieren, mit besonderer Beriicksichtigung, u. s. w. Jahrb. Wiss.
Tiersucht, Hanover, Bd. 5, S. 94. Brandt, J. F. 1900 Zur Phylogenie der Saugethierehaare. Biol. Centralbl.,
Bd. 20. Browne, P. A. 1883 Trichologia Mammalium. Philadelphia. Browne, P. A., and Dickeson, M. VV. 1848 Trichographia Mammalium. Philadelphia. Ehrlich, Krause, Mosse, Rosin, und Weigert 1903 Encyclopadie der
Mikroscopischen Technik. Berlin u. Wien. FoNTES, L. R. deS. 1879 Beitrage zur anatomischen Kenntnis der Hautdecke
des Ornithorhynchus 'paradoxus. Inaug. Diss., Univ. Bonn. Frederic, J. 1906 Sinushaare der Affen. Zeitschr. flir Morph., Stuttgart,
Bd. 9, S. 323. Friedenthal, H. 1906 Ueber die Behaarung des Menschen und auch anderer
Affenarten. Verh. Ges. der Naturfor. Leip., Bd. 79, II, S. 306.
1909 Haarparasiten und Haarbau als Hinweise auf Blutverwandt schaft. Ber. Sits. Ber. Ges. der Naturfor. Fr., S. 379.
1911 Ueber der Behaarung der Menschenaffen und Menschenrassen.
Zeitschr. Ethn. Ber., "Bd. 43. S. 974.
486 LEON AUGUSTUS HAUSMAN
Friedexthal. H. 1911 Zur Technik der Untorsuclmiifi; ilcs Haaiklcidcs uiid
der Haare dcr Saiigctiere. Zcitschr. I'iir AIoipli. u. AnlliiDp., Ud. 14, ♦ S.441.
1911 Tierhaaratliis. Jena. Garcia, S. A. 1892 Beitra}j;e zur Kenntnis dcs naanvcclisclslKM iiuMischlichen
Embryonen und Neugeborenen. M()ii)li. Ail)., Hd. 1. Glockxer, E. F. 1819 Ubcr dio Haare des Ornilhorhijnahii-s. Isis, 8. 651. Hager, H., axd Mez, C. 1899 DasMikroscop und seine Anwendung. Berlin. Hesse uxd Dofleix 1914 Tierbau und Tierleben. Leip. u. Berlin. Home 1802 A description of the anatomy of Ornithorh!jn':hu.s paiado.vas.
Phil. Trans., p. 67. Japha, A. 1911 Die Haare der Waltiere. Zool. Jahrb. (Anat.), Bd. 32.
1911 Ueber die Haare der Wale. Verb. Ges. der Naturfor., Leip.,
Bd. 82, S. 168. Kazzaxder, J. 1910 Nochmals zur Biologic der Talpn ciiropaca (Haarapparat
am Fuss). Anat. Anz., Jena, Bd. 37, S. 4. Keibel, F. 1895 Ontogenie und Phylogenie von Haar und Feder. Ergb. der
Anat., Bd. 5, S. 619. KiDD, W. 1901 Use inheritance illustrated by the direction of the hair on the
bodies of animals. London.
1902 Hair slope in connection with habits. Proc. Zool. Soc, Lond., vol. 2, p. 145.
1903 Notes on the hair slope of four typical mammals (otter, dog, ox, and horse). Proc. Zool. Soc, Lond., vol. 1, p. 79.
1914 The direction of hair in animals and man. New York. Kukexthal, W. 1909 Untersuchungen an Walen. Jen. Zcitschr. flir Natur wiss., Bd. 45, S. 545. Lampert, M. 1910 Contributions a I'etude des polls de I'homme et des ani maux. Paris. Laxgley J. N. 1901 Practical histology.
Latteux, p. 1887 Manuel de technique microscopique. Paris. Leydig 1859 Ueber die ausseren Bedeckungen der Siiugethiere. Archiv. ftir
Anat. Phys. u. Wiss. Med., S. 677. Lorexz, L. 1909 Betrachtung ueber das Haarkleid der Saugetiere. Verb, der
Zool.-Bot. Gesell. zu Wein., Bd. 59 S. 271. Meckel 1826 Ondthorhynchi paradoxi Descrijitio Anatomica. Meijere 1894 Ueber die Haare der Siiugethiere, besonders ueber ihre .\nord nung. Morph. Jahrb., Bd. 21, S. 312. Mertschixg, a. 1888 Beitriigc zur Histologic des Haares und llaarbalges.
Archiv fiir mikr. Anat., Bd. 31, S. 32. Meyer-Lierheim, F. 1910 Die Dichtigkeit der Behaarung beim Fetus des Men schcn und dcr Affcn. Zcitschr. Morph., Stuttgart, Bd. 13, S. 131. Perox et Lessueur Voyage dc Decouvertes aux Terrc Australc pendant les
anncs 1880-1884. PiXKUS, F. 1906 Ueber der Haarscheiben dcr Monotremen. Zool. Forschungs rcisen in .Australien und dcni malayischcn Archipel, R. Scmon, 3.
Band, 3. Licfcrung (in Dcnkschr. dcr MchI. Naturwiss. Gesell., Jena),
HAIR STRUCTURE OF THE MONOTREMATA
487
PouLTON 1894 Structure of the bill and hairs of Ornilhorhynchus paradoxus, etc. Quart. Jour. Mic. Sci., p. 143.
Rawitz, B. 1906 Beitrage zur mikroscopischen Anatomie der Cetaceen (Ueber der Feineren Bau der Haare, u. s. w.). Intern. Monatschr., Anat., Leip., Bd. 23, S. 19.
RoMER, F. 1898 Studien ueber das Integument der Saugetiere. II. Das Integument der Monotremen. Zool. Forschungsreisen in Australien und dem malayischen Archipel, R. Semon, 3. Band, 2. Lieferung (in Denkschr. der Med. Naturwiss. Gesell., Jena).
Sarasin, p. 1912 Ueber die zoologsiche Schatzung der sogenanten Haarmenschcn. u. s. w. Zool. Jahrb. Suppl., S. 289.
ScHWALBE, G. 1909 Ueber die Richtung der Haare bei Saugetiere, speziell beim Menschen. Miincher med. Wochenschr., Bd. 56, S. 315.
1911 Ueber die Richtung der Haare bei den Affenembryonen, u. s. w.
1912 Mitteilungen ueber die Haare, besonders ueber ihre Richtung. Mitt. Philomath. Ges. Strass., Bd. 4, S. 517.
Spencer and Sweet 1898-99 The structure and development of the hairs of
monotremes and marsupials. Part I. Monotremes. Quart. Jour.
Mic. Sci., p. 549. ToLDT, K. JUN. 1905 Ueber das Genus Proechidna. Ver. der E. K. Zool.
Bot. Gesell. zu. Wien, Bd. 55, S. 5.
1906 Ueber das Haar- und Stachelkleid on Zaglossus, Gill {Proechidna
Gervais). Ann. des K. K. Naturhist. Hofmus, Bd. 21, S. 1.
1906 Interessante Haarformen bei einem kurzschnabeligenAmeiseni gel. Zool. Anz., Bd. 30, S. 305.
1907-08 Studien ueber das Haarkleid von Vulpesvulpes, L. Ann. des
K. K. Naturhist Hofmus. Wien, Bd. 22, S. 197.
1909 Betrachtung liber das Haarkleid der Saugetiere. Wien. Verh. Zool. Bot. Gesell., Bd. 59, S. 271.
1910 Ueber cine Beachtenswerte Haarsorte und ueber das Haarfort mensystem der Saugetiere. Wien Ann. Naturhist. Hofmus., Bd. 24,
S. 195.
1912 Beitrage zur Kenntnis der Bahaarung der Saugetiere. Zool.
Jahrb. Jena, Abt. f. Sys., Bd. 33, S. 9.
1912 Epidermusstreifen, Haareiben, und Wiltzeichnung in der Entwicklung der Hauskatze. Wien. Verh. Zool. Bot. Gesell., Bd. 16.
1913 Ueber die aussere Korpergestalt eines Fetus von Elephas tnaximus. Wien, Denkschr. der Akad. Wiss. Med. Nat. Klasse, Bd. 90, S. 259.
VAN DE Hoeven 1823 Memoire sur le Genre Ornithorhynque, Nova Acta.
Acad. Caes. Leop., vol. 11, p. 351. Waldeyer 1884 Atlas der menschlichen und tierischen Haare, sowie der Jihn lichen Fasergebilde. Lahr. Weber, M. 1904 Die Saugethiere. Jena.
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, NO. 4
PLATP 1
EXPLANATION OF FIGURES
I Outline drawing of Ornithurhynahus anatinii!<, to show the location of the various hair tracts. A, modified shield hair of the chin; B, fur hair of the ear; C, area of pigmented, truncated shield hair; D, area of unpigmented, truncated shield hair; E, truncated shield hairs of feet and venter of tail; F, shield hair of dorsum; G, large shield hair of dorsum of tail. The areas E and G lack the fur hair. None of the areas are sharply defined (with the exception of the area of the ear), but merge gradually into one another. X |.
2 Arrangement of the follicles of the shield hair and fur hair on the dorsum (after Meijere). A, shield hair; B, bundles of fur hair. X 200.
3 to 11 illustrate the various types of hair found on Ornithorhynchus (cir. nat. size).
3 Shield hair from the dorsum.
4 Shield hair from midway between the eyes.
5 Shield hair from the proximal end of the tail.
6 Shield hair from the distal end of the tail.
7 Shield hair from the venter.
8 Modified shield hair from the chin.
9 Fur hair of the dorsum and venter. 10 Fur hair from the area of the ear.
II Shield hair from the area of the ear.
12 Guide figure.
13 Shield hair at point o, figure 12, showing the cuticular scales. M, medulla ; CO, cortex. X 800.
14 Shield hair at m-7i, figure 12. B, shaft; C, isthmus; D, shield; iU, medulla; CO, cortex. X 800.
15 Shaft of shield hair at p, figure 12. M, medulla; CO, cortex. X 800.
16 Shaft of shield hair below q, figure 12. B, bulb; M, medulla; CO, cortex. X 800.
17 Shield of shield hair. M, medulla ; CO, cortex ; CU, cuticle ; M', vestiges of the medulla which often persist near the base of the shield. X 400. .
18 Guide figure.
19 Transverse section through various portions of the shield as shown by the guide figure, figure 18. Letters indicate where the sections were made. Note the greater thickness of the cuticle on the ectal surface of the shield. X 90.
20 Transverse sections through the shaft of the shield hair, midway from the base of the shaft to the isthmus. M, medulla; CU, cuticle; CO. cortex. X 280.
21 Transverse section through the shaft of the shield hair near the base of the shaft just above the mouth of the follicle. M, medulla; CU, cuticle; CO, cortex. X 280.
22 Shaft of the shield hair, dissected. CU, cuticle, intact; CO, long distorted cells of the cortex exposed, after the removal of the cuticular scales; M, medullary colls exposed after the removal of the cortex element. X 2100.
488
HAIR STRUCTURE OF THE MONOTREMATA
LEON AUGUSTUS HAUSMAN
PLATE I
PLATE 2
EXPLANATION OF FIGURES
23 Medulla of the shield hair in the shaft below the isthmus. M, medullary cell; I, interstitial or intermedullary space. X 4000.
24 Medulla of the shield hair midway between the isthmus and the tip of the shield. M, medullary cell. X 200.
25 Shield hair of the tail, near the base. X 535.
26 Shield hair of the tail, midway from base to tip. M, medulla. X 45.
27 Shield hair of the feet, midway from base to tip. M, medulla. X 45.
28 Section through the shield hair of the tail, midway from base to tip. M, medulla; CU, cuticle; CO, cortex. X 73.
29 Section through shield hair of the feet, midway from base to tip. M, medulla; CU, cuticle; CO, cortex. X 73.
30 ShoAving the relations of the shield and fur hair on the dorsum of Ornithorhynchus. A, shield hair; B, fur hair; C, skin. X 5.
31 Showing the relations of the modified shield and fur hair on the chin area of Ornithorhynchus. A, modified shield hair; B, fur hair; C, skin. X ^.
32 Guide figure.
33 Modified shield hair of chin, at A, figure 32. X 200.
34 Modified shield hair of chin, at B, figure 32. M, medulla. X 210.
35 Modified shield hair of chin, below C, figure 32. X 200.
36 Guide figure.
37 Fur hair, A-B, figure 36. X 450.
38 Fur hair, C-D, figure 36. X 600.
39 Single, isolated cuticular scale from the shaft of the fur hair, near base. X 1250.
40 Fur hair at the base. M, medulla; CU, cuticle; CO, cortex. X 650.
41 Transverse section through the shaft of the fur hair, midway between the base and tip. M, medulla; CU, cuticle; CO, cortex. X 700.
42 Shaft of the fur hair, midway between the base and tip. M, medulla; CU, cuticle; CO, cortex. X 750.
490
HAIR STRUCTURE OF THE MONOTREMATA
LEOX AUGUSTUS HAUSMAN
PLATE 2
cy
CO
28
33
CX)
-A i— B
— c
36
M
CU
29
H=3
•===
RH-m 37
39
41
° u
491
PLATE 3
EXPLANATION OF FIGURES
43 Outline drawing of Tachyglossus hystrix, to show the location of the various spine and hair tracts. A, small spines of the auricular depression; B and B', curved spines and spiny hairs of the flanks; C and C, curved spines and spin}' hairs of the feet; D, caudal si)ines; E, wavy hair of the auricular depression; F, hip tufts of spines; G, large spines and hairs of the dorsum; H, short spines and spiny hairs of the head; /, long spiny and wavy hairs of the venter. X ',.
44 Arrangement of spines and hairs ui>on the dorsum and sides of Tachyglossus (after Romer). X i 45 Small wavy hair from the venter. X 5.
46 Long wavy hair from the venter. X ^.
47 Long spiny hair from the venter. X §.
48 Long spiny hair from venter. X |.
49 Curved spiny hair from fore flank. X h.
50 Small spin§ from fore flank. X |.
51 Small spine from near auricular depression. X h.
52 Large spine from dorsum. X 5.
53 Large spine from hip tuft. X i.
54 Largest of the spines from near the median line of the dorsum. A, pigmented portion; B, unpigmented portion; C, isthmus; D to E, portion within the follicle (bulb). X h.
55 Largest of the spines from the hip tufts, or from the lateral caudal tufts. A, pigmented portion; B, unpigmented portion; C, isthmus; D to E, portion within the follicle (bulb). X 5.
56 Smaller, 'black spine' from near the median line of the dorsum, or from the median dorsal line of the tail. A, pigmented portion; B, unpigmented portion; C, isthmus; D to E, portion within follicle (bulb). X |.
57 Smallest of the spines of the body, unpigmented, and more acuminate than any of the others, from the sides of the body, top of the head, auricular depression, or periphery of tail. B, unpigmented portion; C, isthmus; D to E, portion within the follicle (bulb). X i
58 Flattened, smewhat spiny hair, from near the median line of the dorsum.
A, top of view; B, lateral view. X l^.
59 Slightly finer wavy hair from near the side of the body where the smaller spines begin to appear. A, top view; B, lateral view. (cir. nat. size.)
60 Slender, pigmented spine, from lateral caudal tuft. A, pigmented portion;
B, unpigmented portion; C, isthmus; D to E, portion within the follicle (bulb). Xh
61 Slender, unpigmented spine, from lateral caudal tuft. B, unpigmented portion; C, isthmus; D to E, portion within the follicle (bulb). X h
62 Small spine from top or sides of head, or from the auricular depression. B, unpigmented portion; C, isthmus; D, portion within the follicle (bulb). X 2.
63, 64, and 65 Forms of the spiny hairs of the head. C, isthmus; D, portion within the follicle (bulb). X 2^-.
66 Wavy hairs from beneath the spines and spiny hairs and from the auricular depression. D, portion within the follicle (bulb), (cir. nat. size.)
67 Long spiny hairs, the longest on the body, from the venter. A, top view; B, lateral view; C, isthmus; D, j)ortion within the follicle (bulb), (cir. nat. size.)
68 Short spiny, somewhat wavy hairs, from the venter. A, top view; B, lateral view; C, isthmus; D, portion within the follicle (bulb). X I5,
69 Long wavy hairs, the longest on the body from venter. X' |.
70 Guide figure.
71 Tip of flattened si)iny hair from near the median line of the dorsum, from A-B, figure 70. X 170.
72 Section of the same hair between B-C, figure 70. M, medulla. X 120.
73 Section of the same hair, between C-D, figure 70. M, medulla. X 120.
492
HAIR STRUCTURE OF THE MONOTREMATA
LEON AUGUSTUS HAUSMAN
PLATE 3
73 M
493
PLATE 4
EXPLANATION OF FIGURES
74 Section of the same hair, between D-E, figure 70. M, medulla. X 120.
75 Section of the same hair, between E-F, figure 70. M, medulla X 120.
76 Cuticular scales of the same hair, midway between the base and tip. X 175.
77 Guide figure.
78 Section of the spiny flattened hair of the top of the head, between B-C, figure 77. M, medulla. X 20.
79 Section of the same hair, betwen C-D, figure 77. M, medulla. X 22.
80 Bulb of the same hair, at F, figure 77. M, medulla; S, level of the epidermis (mouth of the follicle). X 32.
81 Cuticular scales of the same hair at point D, figure 77. X 20.
82 Section of the same hair, nearD, figurs 77, showing the isolated group of adventitious medullary cells sometimes present in different portions of the shaft. M, medullary cells. X 27,
83 Guide figure.
84 Tip of the wavy hair from the auricular depression, at the pigmented portion, A-B, figure 83. M, medulla. X 500.
85 Section of the same hair, between B-C, figure 83. M, medulla; Cf/, cuticle; CO, cortex. X 450.
86 Section of the same hair, at D, figure 83. M, medulla; CU, cuticle; CO, cortex. X 450.
87 Cuticular scales of the same hair, midway between C-D, figure 83. X 500.
88 Shaft of the flattened spiny hair of the venter, midway between the base and tip. X 18.
89 Shaft of the same hair, near the base. M, medulla. X 18.
90 Shaft of the long wavy hair of the venter, midway between the base and tip. X 40.
91 Shaft of the same hair near the bas6. M, medulla. X 40.
92 Transverse section of the spiny flattened hair of the venter, midway between the base and tip. CU, cuticle; CO, cortex. X 20.
93 Transverse section of the same hair near the base. CU, cuticle; CO, cortex. X 20.
94 Median longitudinal section through large spine of the dorsum, midway between the base and tip. M, medulla; CU, cuticle; CO, cortex. X 4.
95 Median longitudinal section through the tip of the same spine. M, medulla; CU, cuticle; CO, cortex. X 4.
96 Transverse section through same spine, midway between the base and tip. M, medulla; CU, cuticle; CO, cortex. X 4.
97 Showing the cuticular scales near the base of the same spine. B, i)ortion within the follicle (bulb). X 4.
98 Stereogram of portion of dorsal spine, sectioned, and with the ectal end broken. The method of fracturing may be indicative of the form of the horny, coalesced, fusiform corticular cells which compose the cortex of the spine. M, medulla; CU, cuticle; CO, cortex; B.CO, broken cortex. X 4.
494
HAIR STRUCTURE OF THE MONOTREMATA
LEON AUGUSTUS HAUSMAN'
PLATE 4
SUBJECT AND AUTHOR INDEX
ACTIVITY on the part of the giant-cells, and to the significance of the so-called mitotic figures in these cells. Further studies on red bone-marrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular
hemocy togenic • 287
A mphibian larvae to injected croton oil (aseptic inflammation). Reactions of cells in
the tail of 221
Ar.\i, Hayato. On the postnatal development of the ovary (albino rat), with especial reference to the number of ova. . . . 40.5 Atria. Heart, musculature of the 255
BANDS and intercalated discs. Studies on striped muscle structure. VI. The comparative histology of the leg and wing muscle of the wasp, with special reference tothe phenomenon of stripe reversal during contraction and to the genetic relation between contraction 1
Baumgartnek, E. a., Nelson, M. T., and Dock, Wm. Development of the uterine glands in man 207
Begg, Alexander S. Absence of the vena cava inferior in a 12-mm. pig embryo, associated with the drainage of the portal system into the cardinal system 395
Bone-marrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular hemocytogenic activity on the part of the giant-cells, and to the significance of the so-called mitotic figures in these cells. Further studies on red 287
CARDIN.\L system. Absence of the vena cava inferior in a 12-mm. pig embryo, associated with the drainage of the portal system into the 395
Cava inferior in a 12-mm. pig embryo, associated with the drainage of the portal system into the cardinal system. Absence of the vena 395
Cells, and to the significance of the so-called mitotic figures in these cells. Further studies on red bone-marrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular hemocytogenic activity on the part of the giant . . 287
Cells in the tail of Amphibian larvae to injected croton oil (aseptic inflammation). Reactions of 221
Clark, Eleanor Linton, Clark, Eliot R., and. Reactions of cells in the tail of Amphibian larvae to injected croton oil (aseptic inflammation) 221
Clark, Eliot R , and Clark, Eleanor Linton. Reactions of cells in the tail of Amphibian larvae to injected croton oil (aseptic inflammation) 221
Content of the kidney tubule. A study of the lipoid 69
Contraction bands and intercalated discs. iStudies on striped muscle structure. VI. The comparative histology of the leg and wing muscle of the wasp, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relation between 1
Croton oil (aseptic inflammation). _ Reactions of cells in the tail of Amphibian larvae to injected 221
DEVELOPMENT of the ovary (albino rat) , with especial reference to the number of ova. On the postnatal 405
Discs. Studies on striped muscle structure. VI. The comparative histology of the leg and wing muscle of the wasp, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relations between contraction
bands and intercalated 1
Dock, Wm., Baumgartner, E. A., Nelson, M. T., and. Development of the uterine glands in man 207
EMBRYO, associated with the drainage of the portal system into the cardinal system. Absence of the vena cava inferior
in a 12-mm. pig : 395
Evolution in the mammalia. A critique of the theories of pulmonary 99
FIGL^RES in these cells. Further studies on red bone-marrow. I. Experimental. , II. Cytologic, with special reference to the data suggesting intracellular hemocytogenic activity on the part of the giantcells, and to the significance of the socalled mitotic 287
GIANT-CELLS, and to the significance of the so-called mitotic figures in these cells. Further studies on red bone-marmarrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular hemocytogenic
activity on the part of the 287
Glands in man. Development of the uterine 207
HAIR structure of the Monotremata. A micrological investigation of the 463
HauSiMan, Leon Augustus. A micrological investigation of the hair structure of the
Monotremata 463
Heart, musculature of the atria 255
Hemocytogenic activity on the part of the giant-cells, and to the significance of the so-called mitotic figures in these cells. Further studies on red bone-marrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular 287
Human lung. The finer ramifications of the 315 Huntington, Geo. S. A critique of the theories of pulmonary evolution in the mammalia 99
497
498
INDEX
INFERIOR in a 12-miii.pig embryo, associated with the drainage of the portal system into the cardinal system. Absence of the vena cava .• 395
Inflammation). Reactions of cells in the tail of Amphibian larvae to injected croton oil (aseptic 221
Intercalated discs. Studies on striped muscle structure. VI. The comparative histology of the leg and wing muscle of the wasp, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relation between contraction bands and .■ • • 1
Intracellular hemocytogenic activity on the part of the giant-cells, and to the significance of the so-called mitotic figures in these cells. Further studies on red bonemarrow. I. Experimental. II- Cytologic, with special reference to the data suggesting 287
JORDAN, H. E. Further studies on red bone-marrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular hemocytogenic activity on the part of the giantcells, and to the significance of the
so-called mitotic figures in these cells 287
Jordan, H. E. Studies on striped muscle structure. VI. The comparative histology of the leg and wing muscle of the wasp, with special reference to the phen9menon of stripe reversal during contraction and to the genetic relation between contraction bands and intercalated discs 1
fj-IDNEY tubule. A study of the lipoid fV ( ontent of the 69
LA R\'AE to injected croton oil (aseptic inflanimation"). Reactions of cells in the tail of Amphibian • 221
Leg and wing muscle of the wasp, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relation between contraction bands and intercalated discs. Studies on striped muscle structure. VI. The comparative histology of the 1
Lipoid content of the kidney tubule. A study of the 69
Lung The finer ramifications of the human 315
Lungs. Contributions to the histology of the respiratory spaces of the vertebrate 333
M,\MMAIJA. A critique of the theories of pulmonary evolution in the 99
Marrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular hemocytogenic activity on the part of the giant-cells, and to the significance of the so-called mitotic figures in these cells. Further studies on redbone- 287
Mitotic figures in these cells. Further studies on red bone-marrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular hemocytogenic activity on the part of the giant-cells, and to the significanc(^ of the so-called. . . . 287
Monotremata. A micrological investigation of the hair structure of the 463
Muscle structure. VI. The comparative histology of the leg and wing muscle of the wasp, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relation between contraction bands and intercalated discs. Studies on striped • 1
Musculature of the atria. Heart 255
NELSON, M. T., AND Dock, \Vm., BaimGAiiTNER, E. A. Development of the
uterine glands in man 207
Number of ova. On the postnatal development of the ovary (albino rat), with especial reference to the 405
OGAVV.\, Chikanoscke. Contribution to the histology of the respiratory spaces of
the vertebrate lungs 333
Ogawa, Chikanosuke. The finer ramifications of the human lung 315
Oil (aseptic inflammation). Reactions of cells in the tail of Amphibian larvae to
injected croton 221
Ova. On the postnatal development of the ovary (albino rat), with especial reference
to the number of 405
Ovary (albino rat), with especial reference to the number of ova. On the postnatal development of the 405
PAPEZ, James W. Heart, musculature of the atria 255
Pig embryo, associated with the drainage of the portal system into the cardinal system. Absence of the vena cava inferior in a 12-mm 395
Portal system into the cardinal system. Absence of the vena cava inferior in a 12-mm. pig embryo, associated with the drainage of the 395
Pulmonary evolution in the mammalia. A critique of the theories of '■ .. 99
RAT) , with especial reference to the number of ova. On the postnatal development of the ovary (albino 405
Reactions of cells in the tail of Amphibian larvae to injected croton oil (aseptic inflammation) 221
Red bone-marrow. I. Experimental. II. Cytologic, with special reference to the data suggesting intracellular hemocytogenic activity on the part of the giant-cells, and to the significance of the so-called mitotic figures in these cells. Further studies on 287
Respiratory spaces of the vertebrate lungs. Contributions to the histology of the 333
SMITH, Christianna. A study of the lipoid content of the kidney tubule 69
Spaces of the vertebrate lungs. Contributions to the histology of the respiratory. . . 333
Striped muscle structure. ^T. The comparative histology of the leg and wing muscle of the wasp, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relation between contraction bands and intercalated discs. Studies on 1
Structure of the Monotremata. A micrological investigation of the hair 463
Structure. \T. The comparative histology of the leg and wing muscle of the wasp, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relation between contraction bands and intercalated discs. .Studies on striped muscle 1
System. Absence of the vena cava inferior in a r2-mm. pig embryo, associated with the drainage of the portal system into the cardinal 395
System into the cardinal system. Absence of the vena cava inferior in a 12-mm. pig embryo, associated with the drainage of the portal 395
INDEX
499
TAIL of Amphibian larvae to injected croton oil (aseptic inflammation). Reac- t
tions of cells in the 221
Tubule. A study of the lipoid content of the kidney 69
UTERINE glands in man. Development of the 207
VENA cava inferior in a 12-mm pig embryo, associated with the drainage of the portal system into the cardinal system. Absence of the 395
Vertebrate lungs. Contributions to the histology of the respiratory spaces of the 333
WASP, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relation between contraction bands and intercalated discs. Studies on striped muscle structure. VI. The comparative histology of
the leg and wing muscle of the
Wing muscle of the wasp, with special reference to the phenomenon of stripe reversal during contraction and to the genetic relation between contraction bands and intercalated discs. Studies on striped muscle structure. VI. The comparative histology of the leg and
