View source for Paper - On the postnatal development of the ovary (albino rat), with especial reference to the number of ova (1920)

{{Header}}
{{Ref-Arai1920}}
{| class="wikitable mw-collapsible mw-collapsed"
! Online Editor &nbsp;
|-
| [[file:Mark_Hill.jpg|90px|left]] This historic 1921 paper by Arai describes albino {{rat}} {{ovary}} development.
<br><br>
'''Modern Notes:''' {{ovary}} | {{rat}}
<br>
<br>
{{Rat links}}
<br>
{{Genital Links}}
<br>
|}
{{Historic Disclaimer}}
=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:

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 ('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.

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 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.


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.

==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 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


{{Arai1920 table1}}

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



{{Arai1920 table2}}

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
\


\


/


"-^




>.


M






\






























































































! \


k


















^




—




















-~


















































aL

it


100






w


V




^J






'^'


■



_^








_


_


K.


._


















<

—




— 1


—




H
































_


lU.


_>o.


e:


\








»









c
















^


£

L


_:^




■—


_,


_


J


,„







— .






^


—


^






—


-—




—


_


l;









Pr






—


□






r


L_






































—


— '


—


—


—


—






—


—








—


~




—


—


-"






30000


Number of ova itota


)






















































































































































































































































































25000








































































































































































































20000










































































































































































































\






























15000




























































































10000




s


.<>.


































































































1


























































































5000


_






H










►

L







_
















_


_


_






—


_


,




_


_


_


^






_











_







_


u_


—































^




tl








~




—






h



r


—


—




z^




—


—






=


=z










—




—


—


—


—







_















1








_












h


_


_


_




l

_







1




_









^


_








^


^




^.


^


_


• 1 1



100



200 300



400 500



600



700 800 900 1000

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 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.


{{Arai1920 table3}}

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 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


{{Arai1920 table4}}

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.

1. Immediately after birth both the absolute number of small ova, as well as their percentage values, decrease rapidly, reaching 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.


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 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


{{Arai1920 table5}}

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 sixty-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.


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 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


^


'"


~


20-f u




<




B-=


=

40-60 f










k

^





^


-^








^


-^














































/




%.














^


^










^
































-over bO"






















/








s






^










^


^






Small















50



/




f-^




^












^


-^





















,








^




^


"






































































1 25


■










/










































_






_




_


_


_


_




_


_


_


_


^


~


—


b


^














=.


o



_




_


_






_


_


—


Large

— 1 — 1 —




=r>




—






--1


















—




h





—


—


—


-\





H;


—


t

















~


J










~




—


—


—




—


—








—












,
















































\Kn
















"id/^
















So










^,






































































[_i_Q«rtw v.,*a.r.ht —




« 






«^












































































■












\






































































































\


s














r


















































































(










































^
































































\
































^


^






\










^


»-.






































'"




















■'


—


—




—


•

_


__


r




^











\


















~'


—






__






















~


~"




(


















































V






























""




~~


-^


'•


A

" T -g













.•^


—






'n


.J


-A


-.


,








_,






J


^








-

^_








.^


X—


_


_






































°i












-« 


— '


-t




^




__


__


-(


L.


t


_


—


_


o









































^~




-K








r


























n


























-^















—








—


—


\


—




— '




-9


c










































































































Number of ova itotali










































































































































































































































































































































































































1






































































































\
































































































































































































































































































































































































































































































































\






































































































^








































































































<




































































































































































































"




























-~.


-•







_










^


-•.


i^



\




^










N












^




—


^














































































































~1


—


— .














































































_


_




__




^_


_ ^






„


^


i




_








_





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 OF RATS (AVERAGED 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 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 :


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 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}^

{{Arai1920 table13}}

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.

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 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

{{Arai1920 table15}}

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.


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 follicles 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.


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).

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 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.



==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. 

{{Ref-Felix1912}}

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 fur 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.


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.

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.



{{Footer}}