MUSEUM OF COMPARATIVE ZOOLOGY. 407 



divides into two, usually unequal portions. The escape of two globules, 

 one after the other, was never observed. 



I think these statements about the division of the polar globules would 

 bear the confirmation of renewed observations. 



It is the central part of the star which escapes as a polar globule, and 

 the interior of the globules becomes differentiated into protoplasm and 

 nucleus. 



This last statement, like Flemming's, appears almost to forestall the 

 work of 0. Hertwig, but it will be observed, after all, that there is a 

 wide difference between the differentiation of an excreted corpuscle into 

 nucleus and protoplasm after it is expelled from an egg, and the process 

 of division by which the polar globule is really formed. 



That which remains of the peripheral star, continues Fol, is little by 

 little mingled with the protoplasm ; but the other star, which is more 

 extensive, always occupies the centre of the protoplasm ; its centre be- 

 comes homogeneous, and the «tar gradually disappears. There arises at 

 the centre of this star a homogeneous corpuscle of slightly less refractive 

 power than its vicinage, whether a vesicle or a more or less solid body 

 is hard to say. Soon two or three similar structures make their appear- 

 ance by the side of the first, and from the fusion of all results the " ger- 

 minative vesicle " or nucleus of the fecundated ^^g. 



Fol figures only one case (Cleodora, PI. VII. Fig. 2) in which there is 

 more than a single homogeneous corpuscle of this nature, and only tim 

 are indicated there, one of which we may safely assume is the male pro- 

 nucleus. From a comparison with his other figures of early stages of" 

 Cymbulia, I am almost certain that the nuclear structure {y) represented 

 as occupying the centre of the deeper star in Fig. 2 of his eighth plate is 

 not the female, but the male pronucleus, — in other words, that the aster 

 of which it is the centre has no such genetic connection, as Fol assumes, 

 with the remnant of an aster (a) lying under the polar globule. There 

 are several reasons why it is more consistent to assume that Fol has con- 

 founded these two structures, than to grant that the deep star of the figure 

 referred to is one which took its origin from a division of the first aster. 

 Special attention had not been called to the different origin of these 

 nuclear structures, even by those who had observed them ; again, I know 

 of no parallel case where the female pronucleus lies so much nearer the 

 vegetative than the animal pole of the egg ; and, finally, I believe this 

 assumption explains why Fol allows this nuclear structure to occupy the 

 centre of the stellate figure, a thing which can hardly be predicated of 

 the female pronucleus and its aster before the disappearance of its rays. 



