828 



SPERM, OVA, AND PREGNANCY 



Fig. 14.11. A living rat ovum with cumulus 

 oophorus intact and a fertilizing spermatozoon 

 in the ooplasm (A). B. Living rat ovum with cumu- 

 lus intact and showing the earW development 

 of the male and female pronuclei. X 450. 



matozoa from species to species alone may 

 indicate the existence of a variety of mecha- 

 nisms for penetrating the various barriers 

 encountered before the vitellus can be en- 

 tered. 



Quantitative data on the temporal rela- 

 tionship between ovulation, penetration of 

 sperm, and syngamy are lacking for most 

 mammals. Before this information can be 

 had for any animal, the time of ovulation 

 must be easily and accurately determinable, 

 the rate of ascent of spermatozoa to the site 

 of fertilization must be known, and the rate 



of sperm passage through the cumulus 

 oophorus, zona pellucida, and vitelline mem- 

 brane must be established. Information of 

 this sort is now available for several species, 

 particularly that obtained by the use of 

 phase-contrast microscopy and time-lapse 

 cinemicrophotography in the study of living 

 eggs. These methods have supplemented the 

 earlier observations and made possible a 

 more complete account of the process of 

 fertilization (Austin and Smiles, 1948; Odor 

 and Blandau, 1951; Austin, 1951b, 1952a). 



A. THE CUMULUS OOPHORUS AND 

 SPERM PENETRATION 



The number of layers of cells and the 

 compactness of the cumulus oophorus of 

 newly ovulated eggs varies greatly in dif- 

 ferent animals. Cumulus cells and the muco- 

 polysaccharide matrix enclosing them have 

 been reported as sparse or absent in the 

 tubal eggs of the sheep (Assheton, 1898; 

 McKenzie and Allen, 1933; Clark, 1934), 

 the roe deer (Bischoff, 1854), the cow 

 (Hartman, Lewis, Miller and Swett, 1931 1, 

 the pig (Corner and Amsbaugh, 1917), the 

 horse (Hamilton and Day, 1945), and the 

 opossum (Hartman, 1928). In other species 

 such as the rat, mouse, hamster, mink, rab- 

 bit, monkey, and man (Boyd and Hamilton, 

 1952), many layers of granulosa cells form 

 the cumulus oophorus. Furthermore, in cer- 

 tain rodents the ovulated eggs clump to- 

 gether within the dilated ampullae of the 

 oviducts, greatly increasing the number of 

 cell layers and viscous gels the spermatozoa 

 must penetrate in order to reach the more 

 centrally lying eggs. If attempts are made 

 to remove the cells forming the cumulus of 

 newly ovulated eggs by pulling them away 

 with fine needles, the tenaciousness of this 

 investment is impressive and one wonders 

 how a spermatozoon ever reaches the vitel- 

 lus (Fig. 14.11). 



In the preovulatory follicle the cells of 

 tiie cumulus oophorus become loosened from 

 the follicular wall and somewhat separated 

 one from another. This is seen most spec- 

 tacularly in the guinea pig and cat (Myers, 

 Young, and Dempsey, 1936; Dawson and 

 Friedgood, 1940). The ovum and enveloping 

 cumulus cells have frequently been ob- 

 served to lie free within the antrum before 



