258 



THE CELL 



139 A, B), there is a much smaller spherule, around which the 

 yolk commences to arrange itself in radial stria? (Fig. 140-4), 

 forming a radiated figure (a star) ; this star grows gradually more 

 distinct, and at the same time extends itself farther away from 

 the spherule. Since it seems to be derived from the neck of the 



Fig. 139. A and B represent portions of a section of a fertilised egi< of AsteracantMon . 

 A centrosome (sperm-centrum) has moved out a little in advance of the sperm-nucleus. 

 (After Fol.) 



spermatozoon, Fol has called it the sperm-centrum (male centro- 

 some). A corresponding spherule can be seen close to the egg- 

 nucleus, on that side which is turned away from the sperm- 

 nucleus ; Fol has called this the ovo-centrum (female centrosome). 



A B 



Fig. 140 A Fertilised egg of a Sea-urchin (O. Hertwig, Embryology, Fig. 18). The 

 head of the spermatozoon, which has penetrated into the egg, has been converted into a 

 sperm-nucleus (sfc) surrounded by a protoplasmic radiation, and has approached the egg- 

 nucleus (ek). B Fertilised egg of a Sea-urchin (O. Hertwig, Embryology, Fig. 19). The 

 sperm-nucleus (sfc) and the egg-nucleus (ek) have approached each other, and are both 

 surrounded by a protoplasmic radiation. 



An interesting phenomenon now commences to attract attention 

 (Fig. 140 A, B). The egg- and sperm-nuclei (male and female 

 pro-nuclei) mutually attract each other, as it were simultaneously, 

 and travel through the yolk towards each other with increasing 

 velocity; the sperm-nucleus (sk) with its radiation containing 

 the centrosome always moving in front of it, travels more quickly 

 than the egg-nucleus (ek) with its ovo-centrum. Soon they 



