812 



SPERM, OVA, AND PREGNANCY 



TABLE 14.1 

 Estimates of the diameter of the viteUus of various 



mammalian ova 

 (Modified from C. G. Hartman, Quart. Rev. Biol., 



cell surfaces facing the zona and as the cells 

 recede clue to the thickening of the zona they 

 maintain contact with the vitelline mem- 

 Ijrane (Fig. 14.6). Several investigators have 

 called attention to an agranular layer of 

 cytoplasm of the granulosa cells in contact 

 with the developing zona (Trujillo-Cenoz 

 and Sotelo, 1959; Odor, 1960). This layer 

 may indicate the elaboration of secretory 

 material for the building of the zona pellu- 



cida. The agranular layer is certainly sug- 

 gestive but not conclusive evidence for the 

 follicular cell origin of the zona, for a simi- 

 lar layer of dense substance has been de- 

 scribed just below the oolemmal membrane 

 (Fig. 14.8). Some interpret the granular 

 layer below the plasma membrane of the 

 egg as indicative of the transfer of ma- 

 terial of large molecular weight from the 

 granulosa cells into the egg. 



As the zona pellucida increases in thick- 

 ness the number of microvilli also greatly 

 increase and extend into the zona for ap- 

 i:)roximately one-third of its width (Figs. 

 14.6 and 14.8). In eggs with fully developed 

 zonae pellucidae, membrane profiles of the 

 granulosa cell processes traversing this 

 membrane have been observed in intimate 

 contact with the oolemma (Fig. 14.8) (Ya- 

 mada, Muta, Motomura and Koga, 1957; 

 Odor, 1959; Sotelo and Porter, 1959; Ander- 

 son and Beams, 1960). 



If the living tubal ova of mammals are ex- 

 amined with the phase microscope, the pro- 

 toplasmic extensions of the corona radiata 

 cells also may be seen penetrating the zona 

 pellucida in an obliciue or irregular direction. 

 These canaliculi are the radial striations of 

 the zona pellucida described by Heape 

 (1886) andNagel (1888). 



It is well known that after ovulation and 

 sperm penetration the egg shrinks and the 

 ])eri vitelline space makes its appearance. At 

 this time the surface of the vitellus appears 

 quite smooth with the microvilli no longer 

 demonstrable. 



As mentioned above, the jn'otoplasmic ex- 

 tensions of the corona radiata are in inti- 

 mate contact with the surface of the egg 

 membrane. A number of investigators have 

 described the passage of Golgi material from 

 the follicle cells into the eggs in fixed prep- 

 arations in fishes, reptiles, bii'ds, the sciuirrel, 

 rabbit, and rat (Brambell, 1925; Bhatta- 

 charya. Das and Dutta, 1929; Bhatta- 

 charya, 1931). Zlotnik (1948) described the 

 migration of small .sudanophilic granules 

 from the vicinity of the follicular Golgi ma- 

 terial into the oocytes of the dog, cat, and 

 the rabbit. There is great need for clarifica- 

 tion of the role of the cells of the corona 

 radiata in the transport of various materials 

 into the ooplasm and in the formation of 

 yolk in the mammalian egg (Gatenby and 



