Fertilisation of Egg. 



127 



operandi is a little different from the process which accom- 

 panies the production of the polar bodies. I have said that 

 the process is initiated by the nucleus ; as a matter of fact, it 

 appears, at least often, to commence with the division of the 

 centrosome; but the two statements are not at present 

 irreconcilable, for, after all, the centrosome is not at the time 

 thoroughly understood. When the centrosome has divided, 



Fig. 63. — Ovum of an earthworm, showing entrance of three spermatozoaj marked by 

 a whirlpool- like disturbance of the ovum. (After K. Foote.) 



the chromosome bodies are formed in the nucleus as before, and 

 lie across a spindle (Fig. 64, b) ; the number of chromosomes 

 is, in cases where they have been carefully observed, con- 

 stant and characteristic for a given cell. The chromosomes 

 constantly acquire a V shape, the angle of the V lying 

 towards the centre of the nuclear sphere, the ends being thus 

 peripheral. Now, the process of division of the nucleus does 

 not consist, as in the formation of the polar bodies, by a 



