SUBJECT INDEX 



181 



Vitelline membrane, inhibition of sperm 

 attachment to 88; permeability of 86; 

 sperm penetration through 72, 87-89, 

 92, 93; structure of 56, 86 



block to polyspermy 22, 43, 88, 89 

 Vitellus {see also Cytoplasm), diminution of, 

 dining cleavage 78, 79; sizes of, in 

 different animals 13-15 



contraction of, with: maturation 22, 56, 

 57; non-specific activation 57; sperm 

 penetration 22, 24, 56, 57 



elevation of vitelline surface over matura- 

 tion spindle and sperm head 58 



Yolk, amount and distribution of 15, 52, 53, 

 56, 84; assimilation of, during cleavage 



78; deutoplasmolysis of 54, 55; syn- 

 thesis of 16, 63 

 yolk nucleus 63 



Zona pellucida, chemical and physical pro- 

 perties of 89-91 ; effect of enzymes on 

 90, 91; formation of 89; 'lysin' 92; 

 penetration of, by spermatozoon 72, 

 90, 92; perforation and shedding of, by 

 blastocyst 81, 82; structure of 14 (Fig. 

 10), 56, 80, 89 

 zona reaction 22, 43, 92-95 



Zona radiata 89 



Zygote (see Embryo) 



