GENERAL SKETCH 



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 A'^^ifM, from sections. ( X 400.) 

 . /. Soon after the entrance of the spermatozoon, showing the minute sperm-nucleus at Q., 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-chops. B. Sperm- 

 nucleus (d") 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: ''The 

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

 excepting the centrosome, by zvhich division is initiated. The sperma- 



