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Heredity and Environment 



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 glacialis. 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 (cc) to meet it. (After Fol.) 

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

 (/i) ; middle-piece (hi) ; and tail (/)• E-H, Successive stages in the pene- 



