120 F. M. BAI.FOUR. 



from the egg as the first polar body (Fig. 8). The part of the 

 spindle which remains in the egg becomes directly converted into 

 a second spindle by the elongation of its fibres without passing 

 through a typical nuclear condition. A second polar cell next 

 becomes formed in the same manner as the first (Fig. 9), and 

 the portion of the spindle remaining in the egg becomes con- 

 verted into two or three clear vesicles (Fig. 10) which soon 

 unite to form a single nucleus, the female pronucleus (Fig. 11). 



Tig. 10.— Portion of the ovum of Asterias glacialis after the formation of 

 the second polar cell, showing the part of the spindle remaining in 

 the ovum becoming converted into two clear vesicles. Picric acid 

 preparation (copied from Fol.). 



The two polar cells appear to be situated between two membranes, 

 the outer of which is very delicate and only distinct where it 

 covers the polar cells, while the inner one is thicker and becomes, 

 after impregnation, more distinct and then forms what Fol speaks 

 of as the vitelline membrane. It is clear, as Hertwig has pointed 

 out, that the polar bodies originate by a regular cell division and 

 have the value of cells. 



Tig. 11. — Ovum of Asterias glacialis with the two polar bodies and the 

 female pronucleus surrounded by radial stria;, as seen in the living egg 

 (copied from I'ol.). 



General conclusion. 



Considering how few ova have been adequately investigated 

 with reference to the behaviour of the germinal vesicle any 

 general conclusions which may at present be formed are to be 



