12 



Heredity and Environment 



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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, Astcrias glaciaUs. Only one sperm has penetrated the jelly 

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

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

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

 (/*) ; middle-piece (m) ; and tail (/). E-H, Successive stages in the pene- 



