MUSEUM OF COMPARATIVE ZOOLOGY. 395 



outer surface of the germ. What becomes of them is Hot known with 

 certainty, though numerous small granules scattered between tho tie:^- 

 mentation spheres at a later stage are thought to have possibly resulted 

 from them. 



A nucleus was only once seen in the germ before segmentation, and 

 then not carefully studied. He thinks it certainly had no connection 

 with the germinative vesicle, the latter having been already eliminated. 

 Much of the value of Oellacher's work is due to his employing the sec- 

 tion method with the objects studied. The streaked appearance of the 

 germ as portrayed for two sections ('72^ Figs. 27, 28) is of interest as 

 suggesting the persistence of nuclear matter in the germ, and as possibly 

 showing a gyratory tendency in its substance (Fig. 28) not unlike that 

 seen in Li max. 



Kleinenberg ('72, pp. 42, 46, 47), in his well-known paper on 

 Hydra, describes to some extent the regressive metamorphosis of the 

 germinative vesicle, which occurs long before fecundation. The germi- 

 native dot first becomes disintegrated and dissolved. The vesicle is 

 forced to the external pole of the egg, where it undergoes a fatty degen- 

 eration and finally disappears altogether. A contraction of the vitellus 

 takes place soon after the disappearance of the germinative vesicle, and 

 is uniformly accompanied by the elimination of a few particles of the 

 egg substance, which the author identifies with the polar globules * of 

 other animals. No genetic connection between vesicle and polar glob- 

 ules was discovered. 



Ray Lankester ('7^, p. 85) affirms for Aplysia, that "the germinal 

 vesicle escapes previously to yolk cleavage as the ' Richtungsbliischen.' " 



Notwithstanding his valuable contribution to an intimate knowledge 

 of the nuclear changes during cell division, I think we are justified in 

 presuming that Schneider ('73 p. 113) has overlooked some of the 

 phenomena accompanying the earliest changes of the egg. Biitschli 

 ('76, p. 399) with reason questions the propriety of his calling the 

 nucleus of a fecundated egg the germinative vesicle. In this particular 

 case it would seem as though the egg represented by Schneider in Fig. 

 5. a, Taf. V. embraced still the germinative vesicle, containing, as the 



* The criticism of Biitschli ('76, p. 384), that the existence of a "Pseudozelle 

 (Dotterkern) " in these particles makes it more than probable that they have nothing 

 to do with polar globules, would now be without weight, for it was made at a 

 time when the cell nature of these structures was not understood. The ])robability 

 that these are polar globules receives also a certain amount of confirmation in the 

 recent studies of Korotneff ('76) on Lucernaria, a review of which is given far- 

 ther on. 



