CLEAVAGE PLANE AND ENTRANCE POINT OF SPERM. 2-J.^ 



distant from the egg except at the point of sperm attachment 

 where it is nearer the membrane. Then gradually to the right 

 and left of the point of sperm attachment the perivitelline space 

 becomes greater; the egg elongates along a line through the 

 point of sperm attachment (Fig. 6). \Yith the disappearance of 

 the sperm head within the egg (about fifty minutes after in- 



5 



l-i-.. 5. Alter retraction of cone; membraru -itly 



in tin- I'Ki;. 



1-n. ' 1 wo minutes before sperm is 



this elongated appearance is lo- 7 : the egg 



out. The egg flattens at tin.- animal ]><>|r i Fig. 8) and 

 the polar bodies are given off from a clear apparently yolk-! 

 region of the flattened pole (Fig. 2). Some little time later the 

 tir-a iK.ivage furrow appears and the egg is divided unequally 



I ig. 3). 



Tlu- t'l'-rrvations on the relation of this cleavage to the en- 

 trance-point of tin- spi-rm \\ill be considered under three heads 

 corresponding to the methods used. 



