THE CENTROSOME IN EERTIUZATION 



209 



of the middle-piece is likewise not marked off from the tail, yet as we 

 have seen (p. 165) the centrosome passes into this part of the sperma- 

 tozoon. Kostanecki's later examination of the fertihzation of the 



Fig. 104. — Fertilization of the egg of the parasitic annelid, Myzostoma. [WHEELER.] 

 A. Soon after entrance of tlie spermatozoon ; the sperm-nucleus at cf ; at ? the germinal 

 vesicle ; at c the double centrosome. B. First polar body forming at 9 ; //. the cast-out nucle- 

 olus or germinal spot. C. The polar bodies formed {p.b.) ; germ-nuclei of equal size; at c the 

 centrosomes. D. Approach of the germ-nuclei ; the amphiaster formed. 



same animal ('98), while inconclusive on the main point, leaves little 

 doubt that Wheeler's evidence was equally so ; for he has on the one 

 hand shown that the sperm-nucleus is often accompanied by a sperm- 



