FACTS AND FACTORS OF DEVELOPMENT 



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able from the body of the mother and there is no protoplasmic connec- 

 tion between the two. In mammals generally, including also the human 

 species, not a strand of protoplasm, not a nerve fiber, not a blood vessel 

 passes over from the mother to the embryo; the latter is from the 

 moment of fertilization of the egg a distinct individual with particular 

 individual characteristics, and this is just as true of viviparous animals 



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Pig. 3. Entire Spermatozoon of the Annelid Nereis, showing perforatorium (P) ; 

 head (H) ; middle piece (M) , and tail (T). (From F. R. Lillie.) 

 Figs. 4-5. Two Stages in the Entrance of the Spermatozoon into the Egg 

 of Nereis. Some of the protoplasm of the egg has gathered 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 represent yolk. (From F. R. 

 Lillie.) 



