40 



PHYSICAL BASIS OF HEEEDITY 



half of each goes to one pole, and half to the other pole 

 of the spindle (Fig. 15, b). One end of the spindle pro- 

 trudes from the egg, and around it the protoplasm con- 



Fia. 14 — 06cyte of Ancyracanthus, a; growth period, 6; nucleus with tetrads, c. 



Mulsow.) 



(After 



stricts off (Fig. 15, c) to form the first polar body. About 

 the six ovoidal chromosomes left in the egg a new spindle 

 develops; and these chromosomes become drawn into 

 its equator, where they divide again, half of each going 



P'iG. 15. — Egg of Ancyracanthus with six tetrads, a; egg with first polar spindle, 6," 

 egg after extrusion of first polar body, c; egg with second polar spindle, d; egg after the 

 extrusion of both polar bodies, e. 



to one pole and half to the other (Fig. 15, d). A sec- 

 ond protrusion takes place from the surface of the egg 

 which pinches off to form the second polar body (Fig. 

 15, e). Thus, after two mitotic divisions, the egg has lost 

 three-quarters of its chromatin, but retains half the full 



