4 



i >-H" 



T 



EC 



Figs. 4-5. Two Stages ik the Entrance 

 OF THE Spermatozoon into the Egg of Aereis. 

 Some of the protoplasm of the egg has gath- 

 ered at the point of entrance to form the 

 entrance cone (EC) which, together with the 

 sperm head, moves into the interior of the 

 egg in later stages. The black spheres rep- 

 resent yolk. (From F. R. Lillie.) 

 Fig. 3. Entire Spermatozoon of the Annelid Nereis, 



showing perforatorium (P) ; head (H) ; middle-piece (M), and 



tail (T). (From F. K. Lillie.) 



