GENERAL SKK TCH 



141 



It was Boveri ('87) who first accurately traced the complete history 

 of the centrosome and clearly formulated the facts, proving that in 

 Ascans a single centrosome is brought in by the spermatozoon and 

 that it divides to form two centres about which are developed the two 



Fig. 71. Fertilization of the egg of Nereis, from sections. (X 400.) 



A. Soon "after the entrance of the spermatozoon, showing the minute sperm-nucleus at <\, the 

 germinal vesicle disappearing, and the first polar mitotic figure forming. The empty spaces repre- 

 sent deutoplasm-spheres (slightly swollen by the reagents), the firm circles oil-drops. B. Sperm- 

 nucleus (cf ) advancing, a minute amphiaster in front of it; first polar mitotic figure established; 

 polar concentration of the protoplasm. C. Later stage ; second polar body forming. D. The 

 polar bodies formed; conjugation of the germ-nuclei; the egg-centrosomes and asters have 

 disappeared, leaving only the sperm-amphiaster (cf. Fig. 64). 



asters of the cleavage-figure. He was thus led to the following con- 

 clusion, which I believe still accurately expresses the truth: "Tke 

 ripe egg possesses all of the organs and qualities necessary for division 

 excepting the centrosome, bv ivJiicJi division is initiated. The sperma- 



