814 



SPERM, OVA, AND PREGNANCY 



CQ^ PL EX wpMiT0CH0NDRj4 



/ 



GRANULOSA 

 ^ CELL \ 

 PROCESSES 



Z.R 



MlTdCHONDRIA 





NUCLEUS 



GRANULOSA CELL 



I'H,. 14.8. Small M-cUuii noiii all egg williin a laultilainiiiai l\)lln h in ui,i. w .< .-iu,.ll ,iii,.iiin 

 was present. Continuity and extent of ovular microvilli are well shown. Note dense substance 

 just inside the oolemma. (Courtesy of Dr. L. Odor.) 



within 12 to 24 hours after insemination. 

 Furthermore, if the zona pellucida of a rat 

 ovum is removed mechanically, the ooplasm 

 then lying free in Ringer-Locke's solution 

 will undergo visible plasmolysis within a few 

 minutes. 



The physical properties of the zona pel- 

 lucida vary according to the animal species 

 and the experimental conditions under which 

 the membrane is examined. Ordinarily the 

 zona pellucida of a newly ovulated ovum is 

 glassy, resilient, and tough. It is moderately 

 elastic and may be considerably indented 

 with fine needles without rupturing. Chemi- 

 cally the zona is composed chiefly of neutral 

 or weakly acidic mucoproteins (Leach, 1947; 

 Wislocki, Bunting and Dcmpsey, 1947; Bar- 

 ter, 1948; Leblond, 1950; Konecny, 1959; 

 Da Silva Sasso, 1959). It is exceedingly 

 sensitive to changes in hydrogen ion concen- 

 tration: for example, the rat zona pellucida 

 softens in buffers more acid than pH 5 and 



passes into solution in pH 4.5, but the rab- 

 bit zona rec}uires buffers of pH 3 or lower 

 to accomplish the same effect (Hall, 1935; 

 Braden, 1952). 



The dissolution of the zona may also be 

 effected by hydrogen peroxide and certain 

 other oxidizing and reducing agents. Fur- 

 thermore, the zona pellucida in fresh rat 

 eggs may be dissolved readily by trypsin, 

 chymotrypsin, and mold protease (Braden, 

 1952). In the rabbit the zona is removed by 

 trypsin but is not affected by chymotrypsin 

 or mold protease (Braden, 1952) . These data 

 indicate that in both rat and rabbit ova the 

 zona contains protein, but that the type of 

 protein is not the same in the two species 

 (Chang and Hunt, 1956). In rat eggs which 

 are undergoing cleavage and which are ex- 

 amined immediately after being flushed 

 from the oviduct the external surface of 

 the zona is suflEiciently smooth so that the 

 eggs may roll down the incline of a concave 



