The Eggs of Mammals (1936) 3

From Embryology

Chapter III The Growth of the Ovum

The Eggs of Mammals (1936): Introduction | The Origin of the Definitive Ova | The Growth of the Ovum | The Development and Atresia of Full-Grown Ova and the Problem of Ovarian Parthenogenesis | Methods Employed in the Experimental Manipulation of Mammalian Ova | The Tubal History of Unfertilized Eggs | Fertilization and Cleavage | The Activation of Unfertilized Eggs | The Growth and Implantation of the Blastodermic Vesicle | Summary and Recapitulation | Bibliography | Figures | Historic Disclaimer
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We have seen that the production of ova from the germinal epithehum may proceed in the absence of the hypophysis. But does the formation of mature ova depend upon hypophyseal hormones? It is clear that ovulation and particularly the number of follicles that liberate ova is dependent upon hypophyseal hormones. Does this dependence involve merely a maturation of the follicular apparatus or is the actual growth of the ova also concerned? In fixed material cells distinguishable as primary ova are in the mouse a little less than 7 microns in maximum diameter (Pincus, unpublished data), in the rat 8 microns (Aral, 1920a). They eventually attain maximum diameters of 65 to 70 microns. What are the factors governing the growth of these ova to maximum size?


While direct measurements are unavailable it seems obvious that in hypophysectomized animals the ovum attains the maximum size. Smith (1930) notes that the primary follicles in hypophysectomized rats ^^continually are undergoing development, but invariably undergo atresia not later than the stage of cavity formation." Swezy (1933) notes the presence of a follicle having a diameter of 270 microns in a rat ovary 90 days after hypophysectomy and mentions foUicles with diameters of 200 microns. It is evident from the figure in Selye's (1933) paper that foUicles with antra occur in 43 day old rats hypophysectomized at 18 days of age. In the dwarf mouse the largest follicles are about 200 microns in diameter and contain antra (Pincus, unpublished data).


Now it has been demonstrated (Brambell, 1928) that in the mouse the diameter of the follicle when the ovum is fully grown is 125 microns and in the rat (Parkes, 1931) the maximum diameter of the ovum is attained when the follicle is 160 microns in diameter. Full growth of the ovum, then, is attained just before the time of antrum formation which begins in rats and mice in follicles having diameters of about 200 microns. We may therefore deduce that the ova of hypophysectomized animals attain the dimensions of the mature ova in o\ailating animals, and that the growth of the ova (and early follicular growth) is independent of the hypophysis.


This conclusion is supported by various independent lines of evidence. Aral (1920a) found that ova over 60 ijl in diameter appear in the ovaries of rats between the 15th and 20th days of age. Engle (1931a) found pseudomaturation spindles, which appear only in ova of full size, first evident in 16 day old mice and no follicles more than 180 /z in diameter in 14 day old mice. Smith and Engle (1927) found that 10 day old mice treated with gonad-stimulating pituitary implants had to have daily implants for 5 days in order that full ovarian response should be attained, whereas 17 day old mice showed full response in 36 hours to 3 days. Corey (1928) found practically no ovarian response to pituitary extracts in rats until after the 15th day, and Selye and Collip (1933) found no follicular maturation in 6 to 12 day old rats treated with anterior pituitary-like hormone (see also Zondek, 1931). In rabbits (Hammond and Marshall, 1925) the antrum develops later than the 10-1 1th week of life. Hertz and Hisaw (1934) were able to obtain definite follicular response to follicle-stimulating and luteinizing hormones only in juvenile rabbits (12 to 13 weeks old), not in infantile rabbits. Casida (1935) reports that pig ovaries show definite response to pituitary hormones only when antrumcontaining follicles are present.


Nonetheless, fully potent pituitaries are present in 5 to 8 day old rats (Smith and Engle, 1927; Lipschutz, Kallas and Paez, 1929) as judged by their effects in transplantation to immature recipients. It would seem, then, that the attainment of a certain degree of follicle maturity and full ovum size is necessary before activation of the pituitary hormones can be attained in developing animals. It is to be remembered, however, that the release of substances from the normal gland in vivo and the injection of excised preparations are not comparable phenomena. Furthermore, dwarf mice pituitaries can stimulate ovarian growth in immature recipients (Smith and MacDowell, 1931) yet their follicles do develop to the stage of antrum formation. The absence of eosinophile cells in the pituitaries of dwarf mice may, however, indicate the absence of a necessary link in the chain of steps involved in the hypophysis-gonad relationship. Whatever the effect of ovarian maturation upon the pituitary may be, it is plain that no follicular response to pituitary hormones occurs until the time when full sized ova are present. Does this mean that the maturation of the follicle is dependent initially upon some influence of the ovum, or is the simultaneous development of the ovum to full size and follicular growth to stimulable size a coincidence only? The ovum may grow to full size without an investiture of follicle cells as attested by the frequent presence of such ova in the ovaries of dwarf mice (Pincus, unpublished data). On the other hand, anovular follicles do occur in mammalian ovaries (League and Hartman, 1925) though those of large size represent follicles with completely resorbed ova (Engle, 19276). It is interesting to note also that frequent production of anovular follicles from the germinal epithelium takes place in senile rats (Hargitt, 1930).


Fig. 7. Showing the relation of ovum growth to follicle growth. Data on the mouse. (From Brambell, 1930, courtesy of The Macmillan Company.)


Fig. 8. Same as Fig. 7. Data on the rat. (From the Proceedings of the Royal Society.)


Fig. 9. Same as Fig. 8. Data on the ferret. (From the Proceedings of the Royal Society.)


That the growth of the follicle beyond the antrum stage is independent of the growth of the ovum is amply evident from the data presented by Brambell (1928), Parkes (1931) and Pincus and Enzmann (19366). In Table III are presented the data collected by Parkes on the relation of ovum size to body weight and follicle size in seven species of mammals.


Fig, 10. Same as Fig, 7, Data on the pig, (From the Proceedings of the Royal Society.)


Fig, 11. Same as Fig. 7. Data on the rabbit. The lower curve represents ovum diameter plotted against follicle diameter for the nine types of follicles (see Plate III) distinguished by Pincus and Enzmann, 19366.

Figures 7 to 10 relate the various diameters of ova to the diameters of the enclosing follicles. In the rabbit, Pincus and Enzmann (19366) have identified 9 types of follicles each distinguished by characteristic features of the developing ovum, granulosa and theca (see Plate III). When the mean ovum diameters are plotted against the mean follicle diameters (see Figure 11) the resulting curves essentially resemble those illustrated in previous figures, the full ovum size being attained in follicles of type 5 which just precede antrum formation.


Plate III

The development of the follicle and ovum in mature rabbit does

Fig. 1, Type 1 follicle to the left, type 2 follicle to the right. Nuclei in late condensation of prophase. Fig. 2, Follicle type 3. One row of follicle cells. Fig. 3, follicle type 4. Two rows of follicle cells. Fig. 4, Follicle type 5. Many rows of follicle cells. Nucleus migrating to periphery. Fig. 5, Follicle type 6. Antra forming. Fig. 6, Follicle type 7. Numerous antra. Fig. 7, Follicle type 8. Ovum suspended in "spider web" of follicle cells. Corona formed. Fig. 8, Follicle type 9. Last preovulatory stage. Fig. 9, Showing position of various follicle types beneath the germinal epithelium.


TABLE III

Size of the Graafian Follicle at Various Stages of Its Life-History (From Parkes, 1931)


Species

1

Approximate

Weight of

Young Adult

Female

2

Diameter OF Ovum

3 Diameter of

Follicle WHEN Ovum Is Fully Grown

4

Diameter of

Follicle

when Antrum

Appears

5

Diameter of Follicle at Ovulation


gm.

M

/^

M

mm.

Mouse

2 X 10

70

125

200

0.55

Rat

1.2 X 102

63

160

200

0.90

Ferret

5 X 102

108

170

230

1.4

Rabbit

2 X 103

84

145

250

1.8

Baboon

1.2 X 10^

83

180

310

6.0

Pig

5 X 10^

76

300

400

8.0

Cow

4 X 10^

15.0


The data plotted in this manner give no indication of the absolute rate of growth of ova though the relative growth rates may be deduced from the rising segment of the curves drawn to these data. These first segments are plotted in Figure 12, wherein it might be deduced that the ferret ovum grows at the most rapid rate, the pig ovum at the slowest rate, if comparable rates of follicular growth occur in the various species.

If it be assumed that the various types of follicles described by Pincus and Enzmann represent developments occurring at equal time intervals then the lower curve of Figure 11 may be taken as a representation of the growth curve of the ovum. The sigmoid shape of this curve is in fact reminiscent of general growth curves. It cannot be taken as a true growth curve, however, until the time necessary for the development of each type of follicle is accurately known. Such information might very well be obtained from ovaries subjected to x-irradiation and examined at various intervals after exposure.



110


100


90


60


50


The data of Aral (1920a) give a slight indication of the rate of growth of ova since his tables show no ova above 20 /z in diameter in 1 day rats, the first appearance of 20 to 40 ijl in ova in 3 day rats, the first appearance of 40 to 60 /jl ova in 10 day rats, and ova over 60 ijl in rats over 15 days of age. Thus it may be inferred that growth to full size is attained in a little over two weeks. Whether this time is taken also in adult animals is not known exactly, but the minimum period is at least ten days since irradiated mice produce fertile eggs up to ten days after irradiation (Parkes, 192627). This unplies that there is a sensitive period to x-irradiation in young ova. Marshak (1935) has shown that the pachytene stage of meiosis is especially sensitive to x-rays, and young ova enter into a modified pachytene shortly after leaving the ger- gj^^h^of minal epithelium. mammals.


Not all ova grow to mature size. This is evident at once from Aral's data which show that an average of 0.8 per cent of the ova under 20 /x in diameter attain a diameter greater than 60 fi, and only 2.7 per cent reach 20 to 40 jj. in diameter. The factors concerned in the atresia of young ova are as unknown as those determining their growth.


The absolute size attained by mature ova varies from species to species, but the limits are rather narrow (especially in the placental mammals) when comparison is made with other vertebrates or inveterbrates. Hartman (1929) has extensively reviewed the available data on fixed and living material and has estimated the average size of the Ii\dng OA^m for a number of species making allowance for the degree of shrinkage in fixed preparations. His estimates are given in Table IV. Subsequent measurements on living ova have proved these estimates to be on the whole remarkably exact. An excellent brief account of the comparative morphology of living mammalian ova in several species is given by Streeter (1931).


Same as Fig. 7, showing comparative

the ovum in the various species of

(From the Proceedings of the Royal

TABLE IV

Estimates of the Diameter of Full-Grown Mammalian Ova (From Hartman, 1929)


Animal

Monotremata

Platypus

Echidna

Marsupialia

Dasyurus

Didelphis Edentata

Armadillo Cetacea

Whales Insectivora

Mole (Talpa)

Hedgehog (Erinaceus) Rodentia

Mouse

Rat

Guinea pig Lagomorpha

Rabbit Carnivora

Dog

Cat

Ferret Ungulata

Horse

Sheep

Goat

Pig Cheiroptera

Bat Lemurs

Tarsius Primates

Gibbon

M. rhesus

Gorilla

Man


^losT Pkobable Size OF Egg in Micra


2.5 mm. 3.0 mm.

240 140-160

80

140

125 100

70- 75 70- 75

75- 85

120-130

135-145

120-130

120

135

120

140

120-140

95-105

90

110-120 110-120 130-140 130-140


Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)
The Eggs of Mammals (1936): Introduction | The Origin of the Definitive Ova | The Growth of the Ovum | The Development and Atresia of Full-Grown Ova and the Problem of Ovarian Parthenogenesis | Methods Employed in the Experimental Manipulation of Mammalian Ova | The Tubal History of Unfertilized Eggs | Fertilization and Cleavage | The Activation of Unfertilized Eggs | The Growth and Implantation of the Blastodermic Vesicle | Summary and Recapitulation | Bibliography | Figures | Historic Disclaimer

Cite this page: Hill, M.A. (2018, November 15) Embryology The Eggs of Mammals (1936) 3. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/The_Eggs_of_Mammals_(1936)_3

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