STUDIES OF FERTILIZATION 417 
The fertilization cone is no longer seen in the living egg. But 
the sections show that its substance has become so modified as to 
form a definite cell-organ, which can be followed for some time 
after penetration of the spermatozoon. 
Text fig.2 Egg of Nereis fifteen minutes after insemination inink. The black 
outer circle represents the ink, the clear area between this and the egg is the jelly; 
c.l., cortical layer showing the radiating lines of the emptied alveoli; /. c., fertili- 
zation cone; g.v., germinal vesicle, drawn perhaps a little too strongly; it begins 
to break down about this time;7.c., ink cone; 0, oil drops; pl. m., plasma membrane; 
sp., spermatozodn; v.m., vitelline membrane; y., yolk spherules. 
c. Penetration of the spermatozoén. Following the development 
of the depression in the vitelline membrane consequent upon 
the retraction of the fertilization cone, the perivitelline space 
