MUSEUM OF COMPAKATIVE ZOOLOGY. 433 



retaining the same structure, they are fewer and larger. As they in- 

 crease in size, the corpuscles increase in number. At length there are 

 only two large nuclei, and these finally become united. In Succinea 

 there are never more than two, and they may arise far apart. 



Studies on Rotifera and the pseudova of Aphidse only resulted in show- 

 ing that no elimination took place, although the germinative vesicle un- 

 derwent regressive changes and became indistinguishable. 



On the strength of his own observations upon the fate of the germina- 

 tive vesicle, Btitschli comes to the conclusion that it is possible to explain 

 divergences of opinion, and, in particular, that the steps supposed to be 

 preparatory to division are referable to the formation of a spindle and 

 stellar figures, but that this apparent preparation for division never leads 

 to that definite end, inasmuch as a process of expulsion supervenes. His 

 belief that only the vesicle was expelled, and that the whole of the spin- 

 dle body suffered this fate, compelled Biitschli to assume that, on the one 

 hand, the extruded mass in certain cases (Nephelis) increased in volume 

 by a process of swelling, and that, on the other hand, the germinative 

 vesicle might suffer a reduction in size by the loss of fluid constituents 

 during its conversion into a spindle. Thus were the differences in volume 

 between vesicle, spindle body, and polar globules to be explained. It is 

 now certainly established by his observations, he thinks, that the Rich- 

 tungsblaschen in snails, nematodes, and leeches represent the ejected ger- 

 minative vesicle, and most likely the whole of it, since none of his obser- 

 vations indicate that any remnant of the vesicle is left behind save the fluid 

 elements which escape at the time of its metamorphosis into a spindle. 



Biitschli thinks that the structure held by Oellacher to be the radially 

 striate membrane of the germinative vesicle in the trout should not be 

 interpreted in that way ; on the contrary, it is a modified portion of the 

 yolk, and is to be considered as the equivalent of the radial striations 

 which have been observed by himself and Fol. Such being the case, the 

 real extrusion of the germinative vesicle occurs later than Oellacher 

 maintains, viz. only after fecundation. Numerous other special cases, 

 which appear to controvert his ideas of the connection of fertilization 

 with the extrusion of the vesicle, he thinks can be explained by the fact 

 that the vesicle seems to disappear, but really assumes the spindle condi- 

 : tion, and is not actually eliminated before fecundation. 



In an appendix devoted to a refutation of 0. Hertwig's idea that the 



germinative dot persists as the " Eikern," Biitschli (pp. 432 - 437) ex- 



i presses the opinion that this " egg nucleus " may in the case of Toxo- 



! pueustes represent the whole germinative vesicle, reduced in size after 



VOL. VI. — NO. 12. 28 



