52 



PROBLEMS OF FERTILIZATION 



Fig. 2. — Drawings from 

 photographs of Nereis eggs, 

 in a suspension of India ink 

 in sea-water : a, before in- 

 semination ; h, three minutes 

 after insemination; c, twelve 

 minutes after insemination, 

 a, The uninseminated egg 

 is bounded by a strong mem- 

 brane of almost chitinous 

 consistency; within this is a 

 cortical layer without yolk 

 granules, and of alveolar 

 structure ; h, immediately 

 after attachment of the sper- 

 matozoon (not shown in the 

 figure) the egg extrudes a 

 transparent jelly from the 

 alveoli of the cortical layer; 

 c, the secretion of the jelly 

 is completed; the walls of the 

 emptied alveoli of the corti- 

 cal layer now appear as 

 radiating lines crossing the 

 peri vitelline space. The sper- 

 matozoon is seen (to right) 

 with a cone of ink extending 

 into the jelly where its tail 

 lies; the protoplasm of the 

 egg forms a fertilization cone 

 which crosses the perivitelline 

 space and touches the mem- 

 brane beneath the spermato- 

 zoon. 



