Paper - How Large is the Mammalian Egg?

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Hartman CG. How Large is the Mammalian Egg?: A Review. (1929) Quart. Rev. Biol., 4(3): 373-388.

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This historic 1929 paper by Hartman described the differences in oocyte sizes between the different species. Note that this online version is only at an early draft stage of editing.



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How Large is the Mammalian Egg? A Review

By Carl G. Hartman

Department of Embryology, Carnegie Institution of Washington, Baltimore, Mn.

Introduction

If one sketch the outline of a hen's egg so as to fill a page of this Journal as nearly as possible, the egg of the oviparous Australian mammal Ornithorhynchus, drawn to the same scale, would be represented by the natural size of the hen's egg, the entire opossum egg with its albumen, by a cross-section of the lead in a pencil, the human egg by a period in average sized type.

Within the phylum Vertebrata the differences between the smallest eggs, those of mammals, and the largest is even greater. Thus the eggs of certain “man-eating" sharks (Lamnids) are as much as 220 mm. in diameter. The egg shell of the now exterminated Apyornis measured 350 mm or over a foot in its longest diameter. The ostrich egg is 150 mm in length and has a capacity of 1.2 liters, or over a quart.


In the evolution of mammals, the Monotremes (Ornithorhynchus and Echidna) form an interesting link, for they possess in their hairy covering and milk secreting glands the chief distinguishing class characteristics of mammals. Yet they “lay" large yolk-laden eggs from which the young emerge after a short incubation outside the female's body. From the 15-millimeter egg of Ornithorhynchus and the 15-millimeter egg of Echidna there is a sudden drop to the typical mammalian egg, which measures about one-tenth of a millimeter. It is true that the marsupial eggs show some transitional characters, as for example, the large albumen layer, the shell membrane, and a somewhat richer supply of yolk, as in Dnsyuru: (Hill). But throughout the Eat/aeriez, the mammals above the marsupials, the egg is very uniform, with not much over a twoto-one variation in size (table 8), which holds from rat to man, from bat to horse, from mouse to elephant and whale. The size of the animal bears no relation to the size of the egg.


The comparison between the large yolk laden eggs on the one hand and the human egg or the eggs of most mammals on the other is not fair to the latter group, for these represent only the yolk or "vitellus" of larger eggs. The total diameter of the hen's egg, for example, is due largely to the albumen laid down in the oviduct around the vitellus. The human egg has no such envelope, and this is true of all mammals with the exception of the marsupials and the Lagomorpha (hares and rabbits). Thus the egg of our only marsupial, the opossum, has a thick albumen layer enclosed in a thin shell membrane; the rabbit egg lacks the shell membrane, while all other mammalian eggs have only a highly transparent limiting membrane, or “zona pellucida," which they receive in the ovary before their discharge into the oviduct. The opossum egg, with its opaque white ovum proper in the center of a transparent, hardly visible albumen sphere, looks, in reflected light, much like a grain of sago not quite cooked through—a hyaline sphere with a white spherule in the center.


This comparison between the egg of fowl and that of mammals must be controlled in another way. The yolk or vitellus of the hen's egg is so laden with fat and protein pabulum for the developing embryo that the egg nucleus, with its associated tiny mass of protoplasm, which alone will make the chick embryo, becomes all but lost on the surface of the yolk. But that speck of protoplasm corresponds to the entire Eutherian egg. The reduction in size has, of course, been made possible by the parasitic habit assumed by the mammalian fetus through implantation in the maternal tissues.


In order to visualize for himself the actual size of the mammalian egg, the reader may follow the suggestion which the Berlin anatomist Waldeyer was wont to give his students. Spread out, said he, a sample of sand on a sheet of paper, brush off the easily visible grains and pick out the smallest grain, which it is just possible to see with the naked eye—that speck is of the order of magnitude of the mammalian egg.

The Discovery of the Mammalian Egg

In view of the small size of the mammalian egg, it is not at all surprising that it so long escaped detection. It was not until 182.7 that von Baer announced the discovery of the real mammalian and human eggs. From the time of de Graaf (1673) to that of von Baer the large vesicular follicle of the ovary was regarded as the egg. We now know that the ovarian follicles that bear de Graaf’s name do not constitute the egg but contain the egg. The clear, limpid “graafian” follicles in the ovary of the rabbit, before their dehiscence, do greatly resemble eggs of about eight days’ development, but how such large eggs were to pass through the narrow lumen of the oviduct did not, it seems, concern many investigators. I read, however, in Ritchie's interesting book, Contribution; to Assist the Study of Ovarian Physiology and Pathology (1865) that Morgagni, in his Aoloermria Anatomim Omnia (1741) made the following reflections: “How much more likely is the conjecture that they (the ovarian follicles) are glands secreting fluid for the purpose of keeping the ovum safe, and helping it to escape when the proper time arrives." The error referred to above was a costly one and doubtless retarded progress in the study of embryology during the century preceding von Baer. It is interesting to note that Jones (1837) varied the error of deGraaf by confusing the gelatinous envelope of the rabbit egg with the liquor folliculi. However, the century following the “Father of Embryology,” the nineteenth, did not produce a large array of investigators who occupied themselves with the study of the early stages of the mammalian egg. Without a doubt the outstanding figure was Bischoff, who published, in the forties and following decades, his classical studies on the rabbit, the dog, the guinea-pig, and other domestic animals, as also the deer. These studies have stood the test of time; Bischoff's measurements on the living eggs were the most extensive up to a very recent date.


My calculations of Bischoff’s data are uniformly too high. I have followed Keibel’s equivalent of 3 Prussian Inches (R2,) the equal of 80 mm. This approximates our equivalent of 2.5 mm. for one inch. Thus the average given for the dog egg (1845, page 7) is 0.0068 to 0.0070 P.Z. or 1/13 to 1/12. P.L. or 16 to 19/ 100 mm. These dimensions in Iuicra, according to my calculations would be: 181 to 186, 170 to 184, 166 to 190. It seems that Bischoff attempted exact’ness only in terms of decimal fractions of the P.Z. (preussischer Zoll.). Since his measurements run pretty uniform though high it is probable that the unit of measurement he used was smaller than he thought by a small fraction.


Sobotta (1895) studied 1459 mouse eggs in maturation and early cleavage, and Long and Mark (1911) 1000 mouse eggs in maturation and fertilization. These constitute the most extensive studies of a single species and on a limited phase of development, but they do not include a single measurement on the living egg. As will be pointed out herein, it is the living egg alone that affords the true picture of the egg as a whole and it is only recently that such studies have gotten under way. This fact does not, however, minimize the fundamental processes in the behavior of the egg which only microscopic preparations can disclose; for stained preparations have taught us about the significant behavior of the chromatin, the chief bearer of hereditary characters.

Table 1

From Long and Marie (1911), showing changes in size of the mouse egg during maturation and fertilization, based on eggs fixed in situ

Stage
Number of Eggs Average Diameters in micro
Ovarian:

Germinal vesicle

109 65.5
Beginning of first maturation division 53 62.5
first maturation division 211 58.0
Tubal:

Second spindle

507 55 .6
Second maturation division 36 53.6
Pronuclei 123 54.0
Eggs in oviduct 16.5 hours 50 53.3
Eggs in oviduct 7.9 hours 50 56.5

Table 2

Sizes (in micra) of ovarian and tubal eggs calculated by the present writer from the atlas of van der Stricht (1923) and from his bat paper (1909)

Animal Ovarian Eggs Tubal Eggs
Man 141x113
Dog 111x92 102x87
Cat 95x84 81x77
Guinea pig 77x63 63x58
Bat (1923) 95x78 70x65
Bat (1909) 90x69 66x58
Mouse 8oX62 53x53

Shrinkage of the Tubal Egg

Can we state in definite figures, then, with reasonable accuracy, the dimensions of the ovum in each species of mammal thus far studied? Before answering this question We must further define it. In the first place, We must specify the stage of development considered, for manifestly, sooner or later, the egg begins to grow. In this discussion We shall limit ourselves to the one-celled or undivided stage, or at least to the stage of early cleavage. These alone approximate the freshly discharged egg. Now there is considerable evidence in the literature that the nuclear changes of first maturation division in the ovary, the second division, and fertilization after ovulation involve also changes in the size of the egg, even entirely aside from the small mass of cytoplasm and nuclear material extruded with the polar bodies. Long and Mark state that a maximal size of the egg is reached at the end of the so-called period of growth, while the egg nucleus is in the condition of a vesicle. From this time to fertilization there is a progressive slight shrinkage, after which the egg increases in size with its sojourn in the tube. Long and Mark's figures are quoted in Table I because they are unique in the number of eggs measured and the care with which the work was done.


Lams and Doorme (1907) were probably the first to call attention to this phenomenon, which 0. Van der Stricht, their teacher, believed to be quite general for mammalian eggs. This author also believed that the low- point varies in different mammals, but in view of the condition of the material on which he made his measurements We may well doubt that so nice a point could have been determined‘ by him. That the ovarian egg is generally reported to be larger than the tubal egg there is no doubt, as one can readily see by a study of the literature. Sobotta in 1905 set down the mouse egg at 59 micra for both the ovarian and the tubal stages, but in a later paper he granted 65 to 70 micra to the ovarian, 60 to the tubal ovum. From Van der Stricht's extensive data I have calculated Table 7., from the standpoint of the present comparison. This author's paper of 197.3 constitutes a veritable atlas of the early history of the mammalian egg, based on the most extensive and varied series in the world.


A similar excess in size of ovarian over tubal ova I have reported for the opossum, where, however, the former were measured in situ, the latter after being washed from the tube and studied singly. Other data in the literature were mostly based on material fixed and sectioned, usually in situ. The measurements are thus open to objection; both ovarian and tubal eggs should be studied alive in the same medium. This I have done in the case of the rabbit. Ovarian eggs removed from the right ovary, excised surgically seven hours post coitum, measured on the average 17.7. x 119 micra. Nineteen hours later two eggs Were taken from the left fallopian tube; they were in the two-celled’ stage when removed, but divided again and were four-celled before they could be photographed. They measured 12.4 X 17.4 micra, a little larger than the ovarian eggs. Dr. W. H. Lewis killed a rabbit ten hours post coitum, when some of the eggshad been shed while others were still retained in the follicles. One ovarian egg measured 119, the other 133 micra; the average for tubal ova was 17.4 micra. The progressive changes in size of the mammalian egg, therefore, await more extensive study. This Will be made by better methods in connection with other studies on the egg.


Table 3

Measurements made from photographs of mammalian eggs taken in the living state. Negatives on file at the Carnegie Laboratory of Embryology, Baltimore. Diameter of ovum proper (villetus) or inner diameter of zona. Dimensions in micra

Animal Stage Number of Eggs Average Size Investigator
Rabbit 1-4-celled 6 12.6 Gregory
Early cleavage 2.2 12.4 Lewis
Ovarian 1 119 Lewis
Ovarian 1 133 Lewis
Ovarian 5 12.0 Hartman
2-4-celled 2 12.4 Hartman
Mouse Ovarian 5 95 Hartman
Dog 1-celled tubal 3 12.0 Hartman
Pig 1-celled tubal 4 111 Heuser and Streeter
Cleavage 8 12.1 Heuser and Streeter
Opossum 56 1-celled tubal 2 145 Heuser and Hartman
313 1-celled tubal 2 12.6 x 106 Heuser and Hartman
351 1-celled tubal 11 108 x 100 Heuser and Hartman
336, 337 Cleavage 6 151 x 140 Heuser and Hartman
842. Early tubal 7 157 x 152 Hartman
833 1-celled tubal 2 173 Hartman
766 Uterine 1 141 Hartman
Various litters of opossum Uterine 100 155 Hartman

Table 4

Eggs (vitellus only, or inner diameter of zona) measured in prepared sections affixed ovaries. Sizes in micra

Animal Authority Maximum Minimum Average Remarks

ANDIAL AUTHORITY IMAXIMUM MINIMUM AVERAGE REMARKS

Dasyurus Hill, 1911 7.70 x 7.60 7.80 x 17.6 7.40 Stated

Didelpbis aurita Hill, 1918 — — 147. x 17.9 Stated

Didelplvix 7/irg. Hartman, 1919 185 x 150 — — Stated

Armadillo Newman, 1917. —-— —— 53 Calculated

Mouse Sobotta, 1895 —— — 59 Stated

{ 2: :2 : §§Z‘E:2ff2f;.““°°‘ Gerlaeh, 1906 71 x 55 53 63 x 54 Calculated (few eggs) Kirkham, 1907 —-— — 71 x 64 Calculated (7. eggs) Lams and Doormc I907 —- — 68 Osmic fix., stated

’ — — 67. Non-os. fix., stated

Long and Mark, 1911 77 50 59 Cf. Table 1 Van der Stricht, 197.3 93 x 64 67 x 60 80 x 67. Cf. Table 7. Kremer, 197.4 75 x 75 65 x 55 70 x 70 Calculated

Rat Kirkham and Burr, 1913 77 x 77. 65 x 55 69 x 63 Calculated Sobotta and Burckhard, 65 6o — Stated

1910

Kremer, 197.4 63 x 55 45 x 45 53 x 47 Calculated

Guinea-pig Rein, 1883 —— — 84 From Lams, 1913 Lams and Doormc I907 —-— -— { 83 Osmic flx., stated

’ — —— 79 Non-osmic fix., stated

was 91 2:8 75 §:::::;d.f:;:,fg“°" Lams I913 __ _ { 80 fleming flx.; calculated ’ 70 N on-osmic fix.; calcu. lated

0. Van der Stricht, 197.3 87 x 60 67 x 60 77 x 63 Cf. Table 7.

Dog 0. Van der Stricht, 197.3 17.3 x 87 95 x 80 111 x 97. Cf. Table 7.

Cat R. Van der Stricht, 1911 180 x 98 111 x 90 ~ 7. eggs; calc. Longley, 1911 97. 79 x 74 — Calculated 0. Van der Stricht, 197.3 100 x 90 87 x 81 95 x 84 Calculated

Ferret Robinson, 1918 133 x 116 98 110 Calculated

Horse Hartman —— — 135 Carnegie collection (in

toto prep.) Bat Van Beneden and Julin, 113 90 104 Calculated 1880

0. Van der Stricht, 1969 110 x 105 50 x 44 95 x 78 Many eggs; calculated 0. Van der Stricht, 197.3 97 x 7o 81 x 67 90 x 68 3 eggs; calculated

Human Nagel, 1888 199 x 194 170 x 165 — 7. eggs (with zona) Waldeyer -— — 130 1 egg Bumm (Gynecology) —— — 7.00 Stated (with zona) Késllikcr (Grundriss) —-— — 7.oo Stated (with zona) 0. Van der Stricht, 1905 157 17.0 x 110 140 x 17.1 Calculated from 13 figs. 0. Van der Stricht, 197.3 179 x 103 107 x 97. 141 x 103 Calculated 4 eggs Hartman —-— — 17.0 x 110 1 egg (Carnegie)

Monkey

(M. mmutrinus) Selenka, 1903 —— — Ca. 40 Stated (M. rbmu) Hartman 108 x 100 105 x 90 110 x 93 Carnegie Coll. Gibbon Hartman —-— 87 x 80 — 1 egg (Carnegie Coll.) Gorilla Hartman —— — 90 x 87 1 egg (Carnegie C011.) 378

Table 5

Tubal ova studied in sections after fixation, either in tine ar after firxt being removed from the tube. Starred in the latter case. Size in micro (vitellus or true ovum only)

Animal Authority Maximum Minimum Average Remarks

ANIMAL AUTHORITY mxunm mnmuu AVERAGE nmmgxs Didelphis (opossum) *Hill, 1918 (D. aurita) 170 x 150 117. x 100 17.6 x 117 Cleavage; calculated

Hartman, 1919 (D. 1/irg.) 148 x 17.5 107. x 76 17.7. x 104 Stated Hedgehog *fischer, A. 46 x 40 —— — One 3-celled egg; calculated Baumeister, I913 —— —— 69 x 54 One egg; calculated Mole Heape, 1886 159 C?) 17.0 17.5 Calculated Mouse Sobotta, 1895, 1898 — — 59 to 60 Stated — —— 6 O ' . Lams and Dootmc’ 190 7 { — 5: Nztlifislildcid 1sit:.t;c;lI:ated Gerlach, 1906 68 x 55 48 x 41 60 x 48 Many eggs Anikiew, 1908 60 x 58 — — Calculated Long and Mark, 1911 —— — 55 Cf. Table 1 Kat Sobotta and Burckhard, 60 55 — Stated and calculated 1910 Kirkham and Burt, 1913 67 x 63 55 x 53 61 x 57 Calculated Huber, 1915 70 x 67. Few eggs . O . ._ Guinea-pig Lams and Doormc, 1907 { N:)1:11:sf!'1n:cic, stand 90 x 74 77. x 58 87. x 67 Cale. from figures X Rubaschkin, 1905 530 60 55 — Stated Lams, 1913 60 45 55 Calculated Rabbit *Assheton, 1894 145 130 133 Cale. 7 figs. X 165

Nihoul, 197.6 96 x 97. 86 x 8o 91 x 83 Calc. Benda fix. Dog *0. Van der Stricht, 197.3 117 x 103 83 x 70 107. x 87 Calculated; cf. Table 7. Cat R. Van der Stticht, 1911 114 x 100 89 x 75 105 x 93 Calculated Bonnet, 1897 — -— 100 1 egg ca1c.; fleming fix. Bonnet (text), 197.7. — —— 111 x 106 1 egg calc.

Longley, 1911 — — 99 x 81 Calculated Hill and Tribe, 197.4 90 x 80 69 x 57 87. x 7o Stated Sheep *Assheton, 1898 17.3 105 114 Calculated Pig *Assheton, 1898 116 81 100 x 95 Calculated Deer Keibel, 1901 115 111 x 106 113 x 108 Calculated Bat Van det Stricht, 1909 83 x 73 60 70 x 65 "Selected as typical" Van det Stricht, 197.3 97 x 70 54 x 53 73 x 67. Cf. Table 7. Hartman 87 x 73 Carnegie Coll.; 1 egg Tatsius Hubrecht, 1907. 82. x 70 77. 77 x 71 Calculated Monkey (M. neme:- Selenka, 1903 — — 40 4-celled

trimet)

Shrinkage due to Fixation

The size changes incident to the vital activities of the developing egg, as set forth above, become insignificant when compared with the shrinkage caused by fixing agents and the after-treatment used in making microscopic preparations. Hence we must know under what conditions the eggs are measured. Since the introduction, about 1870, of the paraffin method of section cutting, by which an egg one—tenth of a millimeter may readily be cut into ten or more sections of convenient thickness, the tendency to use the method on all occasions has been overdone, for it has been substituted for the older and, for some purposes, better method of studying the object in the living state. Refined technique has often been made an end in itself, rather than an aid. fixing fluids, too, cause a variable amount of shrinkage, those containing osmic acid the least of all. The rate at which the reagents are changed is another important factor. With the most careful treatment the Writer kept the shrinkage down, for the most part, to about 15 per cent; more speed in handling the material would certainly have resulted at times in a 30 per cent shrinkage, which is not unusual in much of the work published on the mammalian egg. The study of the mouse egg might be cited in this connection. Sobotta (1905) gives 59 micra for the average mouse egg fixed in either ovary or tube, but in a later paper states that 65 to 70 micra is nearer the truth for the ovarian egg. Kirkham (1907), basing his measurements on the living egg, gives 80 micra for the ovarian, 73 to 78 for the tubal egg. The writer recently photographed five ovarian eggs of a field mouse (sp. 2‘) and these averaged 95 micra in diameter. It is therefore evident (and on this point there is no disagreement among the authorities) that the fixed egg is no criterion of normal size of the living, functioning egg.

A further complication is encountered if one attempts to calculate the size of eggs from authors’ illustrations where the magnifications are indicated. Articles that fail to indicate magnifications are, of course, of no avail for the purpose of this study (e.g., Rein, Melissinos). Were we to refrain entirely, however, from making calculations from the illustrations in the literature, there would remain jolly little data. The proneness of authors to let the reader make the calculations for himself is illustrated by Van der Stricht's invitation (192.3, page 2.79): “I shall not speak further about the exact dimensions of the eggs [he had not yet given any ‘exact dimensions’]—it is easy to calculate them from the drawings.” This invitation I have. accepted, as did Corner (Cowdry’s "Special Cytology,” volume II, page 1112.). The results must, however, fall somewhat short of the true diameter of even the fixed egg, for sections are selected that pass through features of interest, namely the egg nucleus, division spindle, and polar bodies. If these landmarks happen to fall in the middle section of the series the section fairly represents the act ual size of the egg; if, on the other hand, the section is a tangential one, the egg is actually larger than the section shows it to be. It is therefore apparent that measurements based on even the best fixed material, especially th-at fixed in situ, fall short of the actual size of the living egg. This is entirely aside from the irregular shapes which the eggs assume when fixed in situ. I have seldom seen a nicely rounded egg fixed and prepared in the fallopian tube of any animal and I presume that Sobotta had the same experience. Nevertheless this author, by “artistic license," pictures his specimens in what he considered their normal rounded shape. His drawings are the illustrations of maturation, fertilization and cleavage of the mammalian egg most used in the embryological textbooks of all countries.

Table 6

Sizes of egg removed from ovary and meamred in living state. Size: in micm. Vitellus (Sea alm Table 3)

Animal Authority Maximum Minimum Average Remarks
Ornithorhynchus Gatenby and Hill, 192.4 4.4 x 4.16 — — 4400 micra mm.
Ornithorhynchus Caldwell, 1887 2.5 mm. — 2.5oo micra
Echidna Caldwell, 1887 3 .0 mm. — 3000 micra
Mouse Kirkham, 1907 80
Guinea-pig Bischoff, 1852. — 75 Calc. from figs. X 350
Reichert, 1861 —- — 87 Calc. from figs. X 32.0 Rein, 18_83 — — 65 Calc. from 1 fig.
Rabbit Bischoff, 1842. 182. 142. - Dog Bischoif, 1845 190 166 — Stated Bischoff, 1844 166 160 — Stated (from polyov. foll.)
Cat Krause, 1838 170 no 144 Six eggs; calculated Longley, 1911 130 105 — Stated
Goat Krause, 1838 185 17.0 3 eggs; calculated
Pig Bischoff, 1844 140 111 Several eggs
Lowery, 1911 157 "Largest of many"
Bat Van Beneden and Julin, 1880 105 1 egg
Macaque Krause, 1838 140 92. 118 3 eggs

The Study of the Living Egg

What were perhaps the beginnings of a new method in the study of the mammalian egg were made in 1918 by Dr. C. H. Heuser, who, with the writer, under the auspices of the Wistar Institute, made a large collection of opossum eggs at the University of Texas. Many batches of eggs and embryos were at that time photographed in physiological salt solution immediately after removal from the animal. With the assistance of Dr. Heuser, at the Carnegie Laboratory of Embryology, many remarkable photographs of the living rabbit egg in cleavage and germ-layer formation have been secured by Dr. P. W. Gregory and others, and negatives of the early stages of living eggs of other mammals are rapidly accumulating. Indeed, at this laboratory Dr. W. H. Lewis is doing pioneer work in the cinematography of the developing rabbit egg, as he is combining tissue culture with motion picture technique. He has thus far succeeded in keeping the egg alive in rabbit blood plasma for over a week and photographing its normal development for over four days—that is, through cleavage and the formation of the seg mentation cavity. The observer may see the entire process before his eyes in a few minutes and much may be learned which would absolutely escape notice by other methods.


Photography thus applied to embryology may therefore be expected to yield valuable results. Certainly, from negatives the size of the eggs may be calculated at one’s leisure. In Table 3 I have given a number of measurements, chiefly of the opossum egg after photographs taken in Texas and of the rabbit egg after photographs taken by Dr. Gregory and Dr. Lewis.


This section on the measurement of the living egg must not be closed without mention of an event of the greatest significance; namely, the discovery of the first human tubal ovum by Edgar Allen and associated surgeons (Dr. Pratt of Detroit and Drs. Newell and Bland of St. Louis). Seven eggs were recovered from six women. The measurements were made on the fresh eggs and are given in Table 7. Previously Corner (197.3) and Allen (197.7) had recovered eggs from the monkey. These were also measured before fixation (Table 7). The egg of Macacus nemestrinns, in the four-celled stage, was studied by Selenka (1903) in the fixed tube and measured in the shrunken state only 40 micra. These cases mark the beginning of the study‘ of the earliest tubal ova in Primates.

Table 7

Tubal ova studied in the living state. Size: in micra. Measurement: of ovum proper or vitellus only, or in a few cases, chiefly early cleavage stages, inner diameter of zona. See also Table 3.

Animal Authority Maximum Minimum Average Remarks

Platypus Burrell, 1927 3.0 mm. — — Whole egg 17 x 14 mm. Echidna Simon, 1894 — —— —- Whole egg 16 x 13 mm. Dasyurus Hill, 1911 300 x 7.90 —— 7.50 x 7.40 Stated Opossum Hartman, 1919 157 x 157. 108 x 100 130 x 17.3 Stated Hedgehog Keibel, 1888 17.0 — no (In toto in OsO4); stated Mouse Kirkham, 1907 78 73 — Stated Rat Bischoff, 1844 — -—— 100 One egg; stated Kirkham and Burr, 1913 — — 79 Stated Guinea-pig Bischofl’, 1857. 106 91 — Stated (3 P.Z. = 80 mm.) Bischoff, 1857. 74 70 77. Calc. from figs. X 350 Bischolf, 1857. — — 75 After Lams Reichert, 1861 — —- 87 After Lams Hensen, 1876 87. 65 75 Calc. from sev. eggs Rabbit Bischoff, 1847. 180 139 160 Stated. Costl, 1834-1849 — — 17.0 Calculated Hensen, 1876 -— — 1o3 x 93 Calc., 1 fig. Gréwsdew, 1896 144 17.0 133 Calc., sev. figs. Dog v. Baer, 187.7 — — 144 "1/15 of a line" Bischoff, 1845 174 17.5 145 "3 P.Z. = 80 mm." Hartman — — 17.0 Carnegie Coll. Cat Longley, 1911 Cf. Table 3 Hill and Tribe, 197.4 153 x 136 119 x 110 130 x 119 6 eggs in osmic fix. Sheep Bischoff, 1844 —~ -—— 140 1 egg; stated Deer Bischoff, 1854 115 Stated Pig Corner and Amsbaugh,1917 145 135 140 14 eggs, 3 litters Heuser and Streeter, 197.8 131 116 17.1 10 eggs, 3 litters Bats Cspp.) Van Beneden, 1911 95 86 91 7. eggs (118, 108 with zona) Monkey Corner, 197.3 86 83 — 7. eggs, degenerating Allen, 197.7 104 87 —-— 7. eggs, degen. Allen, 192.8 104 1 egg, degen. Hartman - — 107 1 egg, degen. Human Allen, et al., 197.8 184 117 137. With zona


Table 8

Interpretive table, giving the reviewer’s estimate of the true average size of tbe egg of various species of mammal thus far studied. Studies on tbe living egg are considered tbe more authoritative and due correction is made for data based on fixed eggs. Dimension of vitellus only. Jenkinson (1915) probably give: size of entire egg.


Animal Most probable size of egg in micro Jenkinson's Table
Monotremata
Platypus 1.5 mm
Echidna 3 .0 mm
Marsupialia
Dasyurus 240 280
Didelphis 140-160 130
Edentata
Armadillo 80
Cetacea
Whales 140
Insectivora
Mole (Talpa) 12.5 90
Hedgehog (Erinaceus) 100 60
Rodentia
Mouse 70-75 60
Rat 70-75
Guinea pig 75-85 80
Lagomorpha
Rabbit 120-130 150
Carnivora
Dog 135-145 180
Cat 120-130
Ferret 120
Ungulata
Horse 135
Sheep 120 150
Goat 140
Pig 120-140
Cheiroptera
Bat 95-105
Lemurs
Tarsius 90
Primates
Gibbon 110-110
M. rhesus 110-120
Gorilla 130-140
Man 130-140
Jenkinson Table - JW. Jenkinson Vertebrate Embryology. (1913) Oxford. (Gives a table of egg sizes.)

Table 8 Reference: Hartman CG. How Large is the Mammalian Egg?: A Review. (1929) Quart. Rev. Biol., 4(3): 373-388.

1929 Hartman - Species Oocyte Sizes  
Animal Most probable size of egg (μm) Jenkinson's Table
Monotremata
Platypus 1.5 mm
Echidna 3 .0 mm
Marsupialia
Dasyurus 240 280
Didelphis 140-160 130
Edentata
Armadillo 80
Cetacea
Whales 140
Insectivora
Mole (Talpa) 12.5 90
Hedgehog (Erinaceus) 100 60
Rodentia
Mouse 70-75 60
Rat 70-75
Guinea pig 75-85 80
Lagomorpha
Rabbit 120-130 150
Carnivora
Dog 135-145 180
Cat 120-130
Ferret 120
Ungulata
Horse 135
Sheep 120 150
Goat 140
Pig 120-140
Cheiroptera
Bat 95-105
Lemurs
Tarsius 90
Primates
Gibbon 110-110
M. rhesus 110-120
Gorilla 130-140
Man 130-140
Jenkinson Table - JW. Jenkinson Vertebrate Embryology. (1913) Oxford. (Gives a table of egg sizes.)

Table 8 Reference: Hartman CG. How Large is the Mammalian Egg?: A Review. (1929) Quart. Rev. Biol., 4(3): 373-388.

The Size of the Mammalian Egg

We now return to the original question, How large is the mammalian egg? The reflections set down in this review force the conclusion that for no species of mammal is there agreement on measurements of the egg. Those reported have a range far in excess of variations in the normal living egg, great as these variations undoubtedly are. Perhaps the smallest and the largest of a given species, that is, the extremes in size range of living eggs, are not viable. But We know nothing about this problem; it is one that only tissue—culture methods can solve. The reviewer has therefore thought it desirable to bring together the data contained in the World's literature (at least in that major portion available to him) on the size of the mammalian egg and to present it for what it is worth. If the figures are unsatisfactory the study will serve to emphasize the need of further work and more careful methods than those employed in respect to the making of measurements in the past. For the convenience of the reader the data have been condensed into Tables 4, 5, 6 and 7, classified according to the headings of the tables. As a summary of the whole the writer has been bold enough tentatively to put down in Table 8 his own ideas as to the normal range of the average or modal egg size for the various species of mammals. The table is based first on the best measurements of the living egg and second on an evaluation of the data given by the various authors, due correction being made for the methods used. The table should, however, be regarded merely as a basis for revision in the future. Nevertheless, a perusal of the figures will show that Van der Stricht was probably right when he stated the human egg to be the largest, that of Muridae the smallest among the mammiferous animals. It is also apparent that the smallest eggs are probably not as small as the former estimates would have them, the largest not as large as previously stated. The mouse egg is nearer 7o than 50 micra, the human egg nearer 150 than zoo. In other Words the table has a tendency to level up the differences in the sizes of mammalian eggs.


finally it is hoped that the appended literature list will prove helpful to those studying the mammalian ovum for thc first time. Studies on the ovum just before and just after its discharge from the ovary Were, of course, considered the essential studies. Others might have been added which give sizes of the ovarian egg incidental to histological studies on the ovaries; but it is believed that the list includes a sufficient number of these. The list of papers and books on tubal ova, practically all of which have been consulted by the writer, is believed to be fairly complete.


List of Literature

ALLEN, EDGAR. 1927. The menstrual cycle in the monkey, Macacus rhesus: Observations on normal animals, the effects of removal of the ovaries and the effects of injections of ovarian and placental extracts into the spayed animals. Contrib. to Embryol. Vol. 19; Carnegie Inst. of Wash. Publ. No. 380, pp. 1-44.

1878. An unfertilized tubal ovum from Macacus rhesus. Anat. Rec., 37: 351-356.

ALLEN, EDGAR, J. P. Pxxrr, Q. U. Nnwunr. and L. BLAND. 197.8. Recovery of human ova from the uterine tubes: time of ovulation in the menstrual cycle. Journ. Am. Med. Assn., 91 (14): 1018.

Amxnzw, A. 1908. Ueber den Ban des Eiprotoplasma und fiber die excentrische Lagerung der Kernflguren in einigen Tubeneiern der Hausmaus (Mus musculus, vat. alba). Anat. Anz., 37.: 320-330.

Assnmox, R. 1894. A re-investigation into the early stages of the development of the rabbit. Quart. Journ. Micr. Sci., 37: 113-164.

1898a. The development of the pig during the first ten days. 15121., 41: 329-359.

1898b. The segmentation of the ovum of the sheep, with observations on the hypothesis of a hypoblastic origin for the trophoblast. 16121., 41: 7.o5—~7.67..

von Bum, KARL ERNST. 187.7. Epistola de ovi mammalium et hominis genesi. (See also B. Ottow, translation into German, 197.7.)

BALLOWITZ, E. 1906. Zur Kenntnis der Eifurchung bei den Insectivoren. Anat. Anz., 7.9: 674. (Prelim. paper; see Baumeister and Kunsenmiiller.)

BARRY, M. 1838. Researches in embryology, first series, Phil. Trans. (Ovarian follicles and eggs.)

1839. Researches in embryology, second series. (first description of cleavage of cytoplasm.) Ibidrm.

1840. Researches in embryology, third series. Ibidam.

1841. Supplementary note to a paper entitled: Researches in embryology, third series: A contribution to thephysiology of the cell. Ihidem, p. 193.

1843. Spermatozoa observed within the mammiferous ovum. Ibidm, p. 33. (See also Phil. Mag., 1843, May, p. 415.)

Baummsnzn, TH. 1913. Die Entwicklungsvorgéinge am Keime des Igels (Erinaceus Europaeus L.) von seinem Uebertritt in den Uterus bis zur Ausbildung des Mesoderms. Zeitschr. f. wiss. Zool., 105: 1-86.

Bwnnxnonn, J. 1888. Ueber die Umkehr der Keimbliitter bei der Scheermaus (Arvicola amphibius, Desm.). Arch. f. Anat. u. Physiol., Anat. Abt., pp. 7.79186. (A 47.-celled stage, 48;», fixed in situ in 50% alcohol.)

Brsc11om=,Tr1. L. W. 1847.. Entwicklungsgeschichte der Sélugethiete und des Menschen. Leipzig.


B1sc1=1o1=r, T11. L. W. 1844. Beweis von der Begattung unabhangiger periodischer Reifun g und Loslosung der Eier der Séiugethiere und des Menschen als die erste Bedingung ihrer Fortpflanzung. Giessen.

1845. Entwicklungsgeschichte des Hundc eies. Braunschweig.

1857.. Entwicklungsgeschichte des Kanincheneies. Braunschweig.

1857.. Entwicklungsgeschichte des Meetschweinchens. Giessen.

1854. Entwicklungsgcschichte des Rehes. Giessen.

1863. Ueber die Rauzeit des Fuchses und die erste Entwicklung seines Eies. Sitz. Ber. d. k. bayrischen Akad. zu Mfinchen.

1863. Ueber die Bildung des Séiugethiereies und seine Stellung in der Zellenlehre.

1877. Historisch-kritische Bemerkungen zu den neuesten Mittheilungen fiber die erste Entwicklung der Siiugethiereier. Mfinchen.

BONNET, R. 1884. Beitriige zur Embryologie der Wiederkiiuer, gewonnen am Schafei. Arch. f. Anat. u. Physiol., Anat. Abth., pp. 17o-7.30. (Later stages cont. ibidem, 1889, pp. 1-76.)

1897. Beitrige zur Embryologie des Hundes. Anat. Hefte, (1. Abt.), 9: 419-517. (Continued ibidem, 1901, vol. 16, pp. 231-337..)

1891 . Grundriss der Entwicklungsgeschichte der Hausthiere. Berlin. 1910. Lehrbuch der Entwicklungsge schichte. 7.nd. ed. 1917.; 4th ed. 197.0; Berlin.

BRANCA, A. 1910. Caracteres des 7. mitoses de maturation chez l'homme. C. R. de l'Assoc. des Anat., p. 5.

BURRELL, HARRY. 197.7. The Platypus: its discovery, zoological position, form and characteristics, habits, life history, etc. Sydney.

CALDWELL, W. H. 1887. The embryology of Monotremata and Marsupalia Part I. Phil. Trans. Roy. Soc., 178B: 463-486. (Brief abstract in Nature, March 31, 1887, which was copied in Amer. Nat. for May, 1887.)

Conmm, G20. W. 197.3. Ovulation and menstruation in Macacus rhesus. Contrib. to Embryol., Vol. 15, Carnegie Inst. of Wash. Pub. No. 337..

CORNER, G110. W., and A. E. AMSBAUGH. 1917. Oestrus and ovulation in swine. Anat. Rec., 17.: 7.87-7.91.

Cos-rn, J. J. M. C. V. 1834. Recherches sur la génération des mammiferes. Paris.

1841. Histoire de la génération et du développement.

1847-59. Histoire générale et particuliere du développement des corps organises. (Text and atlas dated 1849 consulted.)

CRUIKSHANK, WM. 1797. Experiments in which on the third day after impregnation the ova of rabbits were found in the Fallopian tubes; and in the fourth day after impregnation in the uterus itself; with the first appearance of the foetus. Phil. Trans. Roy. Soc., vol. 18, pp. 119-137, abridged ed. of 1809. (first observation of tubal ova; author just missed discovering the history of the egg of the rabbit 30 years later credited to von Baer.) Transl. in Reil’s Archiv f. d. Physiologic, Vol. 3, 1799.

VON’ EBNER, V. 19oo. Ueber das Verhalten der Zona pellucida zum Ei. Anat. Anz., 18: 55-67..

Fxscmm, A. 1905. Zur Kenntnis der Struktur des Oolemmas der Salugetiereierzellen. Anat. Hefte, 1. Abt., 7.9: 557-585 (Heft 89).

GASSMANN, 0. 197.3. Das Schicksal des unbefruchteten Eies des Menschen. Diss., Gottingen. (Rev. in Zentrbl. f. Gyn§ik., 197.5, 49: 393.)

Gxrnunr, J. BRONTE. 197.7.. Some notes on the gametogenesis of Ornithorhynchus paradoxus. Quart. Jour. Micr. Sci., 66: 475-500.

GATENBY, J. Bnomfi, and J. P. HILL. 197.4. On an ovum of Ornithorhynchus exhibiting polar bodies and polyspermy. Quart. Jour. Micr. Sci., 68: 7.7.9-2.38.

Gunmen, L. 1890. Beitréige zur Morphologie und Physiologic des Ovulationsvorganges der Sangetiere. Sitz.-Ber. d. physik-med. Societéit in Erlangen, Heft 7.7., pp. 43-61.

1906. Ueber die Bildung der Richtungs ktirper bei Mus musculus. Festschrift f. Rosen thal, Wiesbaden.

GRAAF, R. 1677.. De mulierum organis generationi inservientibus tradatus novus. Lugd. Batav.

Gxossnn, Ono. 197.7. Friihentwicklung, Eihaut— bildung und Placentation des Menschen und der Séiugetiere. Miinchen.

Gxwsmzw, W. S. 1896. VVrsuche fiber die kiinstliche Befruchtung von Kanincheneiern. Arch. f. Anat. u. Physiol., Anat. Abth, pp. 169-304.

HAACKE, W. 1884. Meine Entdeckung des Eierlegens der Echidna hystrix. Zool. Anz., 7: 647-653 HEAPE, W. The development of the mole (Talpa Europea); the ovarian ovum and segmentation of the ovum. Quart. Journ. Micr. Sci., 7.6: 157-174. (Later stages were described ibidem, 1883, vol. 7.3, pp. 412-457.).

1905. Ovulation and degeneration of ova in the rabbit. Proc. Roy. Soc., 76 : 7.60.

HARTMAN, CARL G. 1919. Studies in the development of the opossum (Didelphis virginiana L.) III. Description of new material on maturation, cleavage, and entoderm formation. IV. The bilaminar blastocyst. Journ. of Morphol., 32.: 1-142.. (See also ibidem, vol. 2.7, pp. 1-83.)

HARTMAN, Cam. G. 192.4. Observations on the viability of themammalian ovum. Amer. Jour. Obst. and Gynec. 7: 1-4. (See also Smith, Septima C.)

HAUSMANN. 1840. Ueber die Zeugung und Entstehung des wahren vveiblichen Eies, etc. Hannover (not accessible.)

Hnxsxm, V. 1876. Beobachtung fiber die Befruchtung und Entwicklung des Kaninchens und Meerschweinchens. Zeitschr. f. Anat. und Entwicklgesch., 1: 2.13-2.73 and 351-42.3. (See also Hensen's Article: “Zeugung" in Hermann's Handbuch f. Physiologie).

Hnusnn, C. H., and Gnono1:'L. Srnnnrnn. 192.8. Early stages in the development of the pig from the period of the initial cell cleavage to the time of the appearance of limb buds. Vol. 2.o, Contrib. to Embryol., Publication of the Carnegie Inst. of Wash. No. 394, pp. 1-30.

HILL, J. P. 1910. The early development of the Marsupalia with especial reference to the native cat (Dasyurus viverrinus). Quart. Jour. Micr. Sci., 56: 1-134.

1918. Some observations on the early development of Didelphys aurita. Quar. Jour. Micr. Sci., 63: 91-139.

HILL, J. P., and .MARG. T111311. 192.4. The early development of the cat (Felis domestica). Quart. Jour. Micr. Sci., 68: 513-602..

Ho1.1., M. 1891. Ueber die menschliche Eizelle. Anat. Anz., 6: 551-556.

1893 . Ueber die Reifung der Eizelle bei den Siiugetieren. Sitz.-Ber. d. kais. Akad. d. Wiss. (Math-naturwiss. Klasse), Wien, Abth. III, 101: 2.49-3o9.

Human, G. CARL. 1915. The development of the albino rat (Mus norvigicus albinus). Journ. of Morph., 2.6: 2.47-387.

Honruzcnr, A. A. W. 1902.. Furchung und Keimblattbildung bei Tarsius spectrum. Verhandl. kon. Akad. van Wetenschapen, Amsterdam. Vol. 8.

1912.. Friihe Entwicklungsstadien des I gels und ihre Bedeutung fiir die Vorgeschichte (Phylogenese) des Amnions. Zoologische J ahrbiicher, Suppl. XV, Festschr. Spengel, 2.: 739-774.

HYRTL, J. 1878. Lehrbuch der Anatomic des Menschen. Wien. (Page 776, description of an alleged human ovum over o.3oo mm. in diam.)

JENKINSON, J. W 19oo. A re-investigation of the early stages of the development of the mouse. Quart. Jour. Micr. Sci., 43: 61-82.

JENKINSON, J. W. 1913. Vertebrate Embryology. Oxford. (Gives a table of egg sizes.)

JONES, Tnos. WHARTON. 1837. On the first changes in the ova of Mammifera in consequence of impregnation, and the mode of origin of the chorion. Phil. Trans. Roy. Soc., 2.: 339-345. (Varied the mistake of deGraaf by confusing the liquor folliculi with gelatinous envelope of the rabbit egg).

1838. On the ova of man and mammiferous brutes as they exist in the ovaries before im pregnation and on the discovery in them of a vesicle. London Med. Gazette. (On the ger minal vesicle of Purkinje).

1885. On the ova of man and the mammifera before and after fecundation. The Lancet, 2.: 2.83-2.84; 332.-333. (Priority claim polemic, chiefly contra Barry; made nice needle dissections of the ovum for study of zona).

K2A'.pvn1.1, J. 1908. Anatomic und Physiologic des Ovariums der Wiederkiiuer und Schweine. Diss. Bern.

1908. Beitrag zur Anatomic und Physiologie der Ovarien der wildlebenden und gezéihmten Wiederkiiuer und Schweine. Handwirtsch. Jahrb. Schweiz, 2.2.: 53-12.9.

KEIBEL, FR. 1888. Zur Entwicklungsgeschichtc des Igels. Anat. Anz., 3: 632-637.

V 1891. Ueber die Entwicklung des Schweines. Anat. Anz., 6: 193-198. (Prelim. Account.)

1894. Studien zur Entwicklungsgeschichte des Schweines (Sus scrofa dom.). Schwalbc's Morphol. Arbeiten, 3: 1-140. (Continued ibidm, 1896, 5: 17-168).

1897. Normentafeln zur Entwicklungsges chichte des Schweines (Sus scrofa dom.). Jena.

1899. Zur Entwicklungsgeschichte des Rehes. Verh. Anatl Ges., Anat. Anz. Ergiinz. Heft, 16: 64.

1901. Friihe Entwicklungsstadien des Rehes und die Gastrulation der Siiuger. Verh. der anat. Gesellsch., Bonn, Anat. Anz., Erginz. Heft, 19: 184-191.

1902. Die Entwicklung des Rehes bis zur Anlage des Mesoblast. Arch. f. Anat. und Physiol., Anat. Abth., pp. 2.92.-314.

Kxnxrum, W. B. 1907a. The maturation of the mouse egg. Biol. Bull., 12.(4): 2.59-2.65.

1907b. Maturation of the egg of the white mouse. Trans. Conn. Acad. of Arts and Sci., 13: 65-87.

K6LL1xnn, ALn1m'r. 1879. Lehrbuch der Entwicklungsgeschichte der Menschen und der hijheren Thiere. Leipzig. 2.nd. ed.


KOLLIKER, ALBERT. 1884. Grundriss der Entwicklungsgeschichte des Menschen und der héiheren Thiere. and ed.

K6x.L1K1=.R, Amamz-r and VON Enmm. 1907.. Handbuch der Gewebelehre des Menschen. 6th ed., vol. 3, pp. 402-404. (Gives 7.7.0 to 37.0}; for the size of the human egg, zona 7 to 11;»; this is clearly far too high an estimate.)

KRAUSE, C. 1837. “Ei der S2'iugethicre;" pp. 26-30 of article: Vermischte Beobachtungen und Bemerkungen. Miil1er's Archiv. pp. 1-36. (Sec tables.)

KREMER, J. 197.4. Das Verhalten der Vorkerne in befruchtetem Ei der Ratte und der Maus, mit besonderer Beriicksichtigung ihrer Nucleolen. Zeitschr. f. mikr.-anat. Forschung, 1(3): 3S3‘39° 197.4b. Studien zur Oogenese der Sangetiere nach Untersuchungen bei der Ratte und Maus. Archiv f. mikr. Anat., 107.: 337-358. (Based on Sobotta's collection of 569 ovarial and 144 tubal eggs of the rat and 1700 ovarial and 67 tubal eggs of the mouse—-total 7.480 eggs).

KuNs1:NMi'11.L1m, M. 1906. Die Eifurchung des Igels (Erinaccus europaeus, L.) Zeitschr. f. wiss. Zool., 85(1): 74-106.

Kvpmuzn, C. 1887.. Das Ei von Arvicola arvalis und die vermeintliche Umkehr der Keimbliitter an denselben. Sitz.—Ber. d. k. bayer. Akad. d. Wiss. zu Miinchen, pp. 67.1-637. (Youngest egg has thickest zona yet reported—3o;/.).

LAFAIX, M. 1911. Contributions :1 l’étude de la fécondation chez les Mammiféres. These No. 314, Paris, 61 pp.

LAMS, H. 1906. Demonstrations £1 l'Assoc. Anat., Bordeaux; C. R. p. 144,

1910. Recherches sur l’oeuf de cobaye (Cavia cobaya), maturation, fécondation, seg mentation. C. R. Assoc. Anat. Bruxelles, pp. 119-116.

1913. Etude de l’oeuf de Cobaye aux premiers stades de Yembryogénese. Arch. de Biol., 7.8: 7.7.9—37.3.

1874. L’oeuf de la rate pendant les premieres phases de son développement avant son arrivée dans l’utérus. C. R. Assoc. Anat., pp. 195-I99 LAMS, H., and J. Doolmfi. 1908. Nouvelles recherches sur la maturation et la fécondation dc l'oeuf des Mammiferes. Arch. dc Biol., 23(2): 259-365. (White mouse and guinea pig).

Lnucxurr, R. 1853. Art.: “Zeugung"in Wagner’s Handbuch der Physiologic, Vol. 4, pp. 707 E. (P. 876 reference to Latheby’s alleged cases of tubal ova in man.)


LEVI, G. 1914. Das Verhalten der Chondriosomen in den friihesten Embryonalstadien der Singetiere. Anat. Anz., 46 : 187-193. (See also next.)

1915. Il comportamento dei condriosomi durante i pit‘: precoci periodi dello sviluppo dei Mammiferi. Arch. f. Zellforschung, 13: 471‘S7-4LONG, J. A. 1917.. The living eggs of rats and mice. Univ. of Calif. Pub. in Zool., 9: 105-136. (See also Mark and Long. N 0 data on sizes.)

LONG, J. A., and Manx, E. L. 1911. The maturation of the egg of the mouse. Carnegie Inst. of Washington Pub. No. 147.. 77. pp. (See also Contrib. No. 7.16 Zool. Lab. Museum of Comp. Zool., Harvard).

LONGLEY, W. H. 1911. The maturation of the egg and ovulation in domestic cat. Amer. Joum. Anat., 17.: 139-168.

Lowmur, L. G. 1911. Prenatal growth of the pig. Am. Jour. Anat., 17.: 107-138.

MARK, E. L., and J. A. LONG. 1917.. Studies on early stages of development in rats and mice. III. The living eggs of rats and mice, with description of apparatus for obtaining and observing them. Contrib. from Zool. Lab. of Museum of Comp. Zool., Harvard College.

MELISSINOS, K. 1907. Die Entwicklung des Eies der Manse von den ersten Furchung-Phéinomenen bis zur Festsetzung der Allantois an der Ectop1acentarplatte. Arch. f. mikr. Anat., 70: 577-618. (No magnifications stated for drawings; no sizes given.)

Minot, C. S. 1889. Segmentation of the ovum, with special reference to the Mammalia. Am. Nat., 7.3: 463-481; 753-769. (Very general; no sizes given.)

Mmo-r, C. S., and E. Tunes. 1905. Normal plates of the development of the rabbit (Lepus cuniculus L.). No. 5 of Keibel's Normentafeln zur Entwicklungsgeschichte der Wirbelthicre.

98 ppNAGEL, W. 1888. Das menschliche Ei. Arch. f. mikr. Anat., 31: 347.—47.3. (Gives complete history of subject to date and good bibliography). NEWMAN, H. H. 1917.. The ovum of the ninebanded armadillo. Growth of the oocytcs, ma turation and fertilization. Biol. Bull., 7.3: roo-140. NIEOUL, J. 197.6. Rechcrches sur l’appareil endo cellulaire dc Golgi dans les premiers stades du développement des Mammiferes. La Cellule, 37: 7.1-40.

VAN OORDT, G. J. 197.1. Early developmental stages of Manis javanica Desm. Verh. kon. Akad. van Wetensch., Amsterdam, Sec. 7., Part XXI, No. 3, 107. pp. (A few shrunken cleavage stages are included.)

Orrow, B. 197.7. Karl Ernst Von Baer's "Ueber die Bildung des Eies der Salugetiere und des Menschen,” mit einer biographischgeschichtlicher Einfiihrung in deutscher Sprache. Voss, Leipzig, 197.7. (Anniversary edition commemorating the centenary of the discovery of the mammalian egg»)

Owmv, R. 1834. On the Ova of Ornithorhynchus paradoxus. Phil. Trans. Roy. Soc., pp. 555-566. Also 1835. On the young of the Ornithorhynchus paradoxus. Trans. Zool. Soc. London, 1: 7.7.7.-7.18.

1868. The Anatomy of Vertebrates. Vol. III, p. 717., quotes egg sizes from Darwin's Variation of Plant: and Animal: under Domesticatian. I have been unable to verify Owen in this quotation from later editions of Darwin's work. Sizes quoted, calculated by myself in micra: man, 141; dog, 158; rabbit, 170; rat, 17.7; mouse, 111; pig, 17.7; cow, 101; guinea pig, 106.

PAINTER, T. 5. 197.8. Cell size and body size in rabbits. Jour. Exp. Zool., 50: 441-454. (Polish rabbit's eggs: 12.0, 17.0, 17.0, 17.6 micraav. 17.1;flemish Giant's eggs; 116, 118, 17.0, 17.0, 17.0, 17.0, I7.6—av. 17.0.)

PATTEN, BRADLEY M. 197.7. The Embryology of the Pig. Philadelphia.

Ponm. 1912.. Unbefruchtetes Ei. Zentrbl. f. Gyn£ik., 46: 1490. (Alleged human eggs.) Rmcnmvr, K.-B. 1861. Beitréige zur Entwicklungsgeschichte des Meerschweinchens. Abhandl. d. k6n. preuss. Akad. d. Wiss., Berlin.

Rum, G. 1883. Beitréige zur Kenntniss der Reifungserscheinungen und Befruchtungsvorgange am Salugethierei. Arch. f. mikr. Anat., 2.7.: 7.33-7.70.

ROBINSON, ARTHUR. 1918. The formation, rupture, and closure of ovarian follicles in ferrets and ferret-polecat hybrids, and some associated phenomena. Trans. Roy. Soc. of Edinburgh, 57.: 303-367..

RUBASCI-IKIN, W. 1905. Ueber die Reifungs- und Befruchtungsprozesse des Meerschweincheneies. Anat. Hefte, 19(3): 507-553.

SAKURAI, TSUNEJIRO. 1906. Normentafel zur Entwicklungsgeschichte des Rehes (Cervus capreolus). F. Keibel, ed., Jena, 100 pp. (Based on Keibel‘s material.)

SALVIN-MOORE, J. E., and F. Tozan. 1908. On the maturation of the ovum in the guinea pig. Proc. Roy. Soc., 80B: 7.85-7.87. (Brief note.)

SCHMALZ, R. 1911. “Die Geschlechtsorgane" in Ellenberger’s Handbuch der vergl. Anat. der 387 Haustiere. Vol. 7., p. 510. (Quotes sizes of eggs of cow, pig, and other mammals).

SCEMALZ, R. 197.1. Das Geschlechtslcben der Haussaugetiere. Berlin. SELENKA, E. 1887. Studien iiber die Entwicklungs geschichte der Thiere. 4. Heft. Das Opossum. Wiesbaden.

1903. Studien, etc. Menschenaffen, etc. 5. Zur vergleichenden Keimesgeschichte der Primaten. pp. 37.9—373. (p. 331: “Eifurchung des Macacus nemestrinus;" a 4-celled egg.)

SEMON, R. 1894. Zur Entwicklungsgeschichte der Monotremen. Zool. Forschungsreisen in Australien und malayischem Archipel. Jena. Bd. II, Lief. 1.

SMITH, SEPTIMA C. 197.5. Degenerative changes in the unfertilized uterine eggs of the opossum, with remarks on the so-called parthenogenesis in mammals. Am. Jour. Anat., 35(1): 81104.

Sosorm, J. 1893. Mitteilungen iiber die Vorgiinge bei der Reifung, Befruchtung und erste Furchung des Eies der Maus. Verh. Anat. Gesell. Gottingen, pp. 111—170.

1894. Die Befruchtung des Eies der Maus. Anat. Anz. 9: 2.2.0-7.2.3 (Prelim. note.)

1895. Die Befruchtung und Furchung des Eies der Maus. Arch. f. mikr. Anat., 45: 15-97.. (The classic on this subject.)

1895. Die Reifung und Befruchtung des Wirbeltiereies. Ergebn. d. Anat. u. Entwick1. Gesch., 5: 507-561. (Rcview.) See also con tinuation, 1906, ibidem, 6: 493-593. (173 titles.)

1907. Die Bildung der Richtungskorper bei der Maus. Anat. Hefte, 35: 493-557.. (Heft 106.)

1908. Ueber die Richtungsteilungen des Siiugetiereies, speziell fiber die Zahl der Rich tungskérper. Verhndl. d. phys.-med. Gesellsch. Wiirzburg, 39: 7.41-7.61.

1901. Die erste Entwicklung des Méiuseeies nach der Furchung. Anat. Anz., Vol. 19, Erganzungsheft, pp. 4-11.

1874. Beitriige zur Furchung des Eies der Séiugetierc mit besondere Beriicksichtigung der Frage der Determination der Furchung. I. Die Furchung des Eies der Maus (Mus musculus). Zeitschr. f. Anat. u. Entwicl<l., 77.: 94-116.

$030114, J., und G. BURCKHARD. 1911. Reifung und Befruchtung des Eies der weissen Ratte. Anat. Hefte, 47.: 433-498.

Span, Gnu F. 1883. Beitrag zur Entwicklungsgeschichte der friiheren Stadien des Meerschweinchens bis zur Vollendung der Keimblase. Archiv f. Anat. u. Physiol., Anat. Abth., pp. 44-60. Sprmcmz, W. B. 1884. The eggs of Monotremes. Nature, 31: 132..

TAFANI, A. 1889. I primi momenti dello sviluppo dei mammiferi. Rendiconti d. R. Accad. dei Lincei (C1. di Sci. mor., stor., e filol.), 5(1): 119-125. (No data on sizes.)

1889. La fécondation et la segmentation étudiées dans les oeufs des rats. Arch. Italiennes de Biol., 11: 112.. (Unillustrated general report.)

1889. La fecondazione e la segmentazione studiate nelle uova dei Topi. Accad. med. fisic., fiorent. (Not available to the present writer.)

VAN BENEDEN, E. 1870. Recherches sur la composition et la significance de l'oeuf. Mém. de l’Acad. roy. de Belgique, Vol. 34.

1875. La maturation de 1'oeuf, 1aféconda tion et les premieres phases du développement embryonaire des Mammiferes d'apres les recherches faites sur la Lapin. Bull. Acad. Roy. des Sci., des Le-ttres et des Beaux-arts de Belgique, 40: 686.

1880. Recherches sur l'embryologie des Mammiféres. La formation des feuillets chez le Lapin. Arch. de Biol., 1: 137-2.2.4. (Con tains frequently copied figures of the rabbit vesicle.)

1899. Recherches sur les premiers stades du développement du Murin (Vespertilio muti nus). Anat. Anz., 16: 307.

1911. De la segmentation, de la formation de la cavité blastodermique et de l'embryon didermique chez le Murin. Arch. de Biol., 2.6: 1-64. (This paper, and the succeeding one on later stages, printed posthumously by Brachet, ibidmz, 1912., 2.7: 191-402., is also a fertile source of illustrations for writers of texts on mammalian embryology.)

VAN BENEDEN, E., and C11. JuL1N. 1880. Observations sur la maturation, la fécondation et la segmentation de l'oeuf chez les Cheiropteres. Arch. de Biol., 1: 551-572..

VAN DER Snucnr, O. 1904. La structure dc l'oeuf des Mammiferes. Premiere partie: L'oocyte au stade de l'accroissement. 1—102..

VAN DER STRICHT, O. 1905. La structure, etc. Deuxieme partie. Structure de l'oeuf de la femme. Bull. de l'Acad. Roy. de Med. de Belgique, Séance Juin 2.4, 1905, pp. 1-35.

1909. La structure, etc. Troisiéme partie. L’oocyte a la fin du stade d'accroissement, au stade de la maturation, au stade de la fécondation et au début de la segmentation (Chauve-souri, Vesperugo noctula). Mém. Acad. Roy. de Belgique, Sér. II, Vol. II, pp. 1-176.

1923. Etude comparée des ovules des Mammiféres aux ditférentes périodes de l'ovogen<‘:se d'apres les travaux du Laboratoire d'Histologie et d'Embryologie de l’Université de Gand. Arch. de Biol., 33: 129-300. 171 figures.

VAN DER STRICHT, R. 1911. Vitellogenése dans l'ovule du chatte. Arch. de Biol., 2.6: 365-481. (Prize essay, Univ. of Gand, 1909.)

WAGNER, Runomnn. 1836. Prodromus historiae generationis hominis atque animalium. Leipzig. (3 tables of measurements of invertebrate and vertebrate eggs, incl.: sheep, 148; rabbit, 148; cat, 150, 110, 2.2.0; rat, 73; bat, 92. micra.)

WALDEYER, W. Eierstock und Ei. Leipzig. 1870. “Die Geschlechtszellen" in Hertwig's Handbuch der vergleichenden und experimentellen Entwicklungslehre der Wirbelthiere. Vol 1, Part 1, pp. 86-476. (P. 32.3: mammalian egg, 100-2.00 micra; hedgehog and mouse, 60; guinea pig, 90; dog and rabbit, 180.)

WEBER, M. 1904. Die Saugetiere. Jena.

WEIL, C. 1873. Beitriige zur Kenntniss der Befruchtung und Entwicklung des Kanincheneies. Stricker's (Wiener) med. J ahrbficher.

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