THE FER T I LIZA TION-PROCESS 





i 



^ 





t 





♦ 6 



iv"^ 



•*►• 









^' <— middle-piece 





.\- tl 



/ 



middle-piece 



-» 



>■ 



y* 



Fig. 



/ 

 29. — History of the middle-piece of the spermatozoon within the egg, 

 Echinarachnius parma. (Original.) 



