12 



Heredity and Environment 



C 





FIG. 4. FERTILIZATION OF THE EGGS OF STAR-FISH AND SEA-URCHIN. 

 A-C, Successive stages in the entrance of a spermatozoon into the egg of 

 the star-fish, Asterias glacialis. Only one sperm has penetrated the jelly 

 layer (//) which surrounds the egg and the peripheral protoplasm (/>/>) of 

 the egg protrudes as an entrance cone (ec) to meet it. (After Fol.) 

 D, Mature spermatozoon of the sea-urchin, Toxopneustes, showing head 

 (/t) ; middle-piece (w) ; and tail (0- E-H, Successive stages in the pene- 



