MUSEUM OF COMPAKATIVE ZOOLOGY. 459 



area" of the first vitelline "sun" (though often observed, this is 

 thought by the author to be without significance) ; but (3.) the greater 

 portion is drawn into the segmentation cavity during the beginning of 

 cleavage, where it helps to form the " Gallertkern. " The " Dotterhiigel " 

 remains, and with some exceptions the plane of the first segmentation 

 passes through it.* 



The author agrees with Fol that the vitelline membrane is not pre- 

 formed, but arises' with the penetration of the first spermatozoon, and 

 thus offers an insurmountable obstacle to the penetration of other 

 spermatozoa. 



KuPFFER UND Benecke C78, p. 21) maintain that in the case of 

 Petromyzon Planeri and P. fluviatilis there are two polar bodies (Kich- 

 tungskorper) eliminated, one before and one after fertilization. As re- 

 gards the former of these, it was first observed after the retraction of 

 the vitellus,t and therefore its origin and the method of its formation 

 were not observed. It was entirely overlooked by both A. Miiller and 

 Calberla. Kupffer and Benecke say (p. 16) that it gives the impression 

 of a nucleus which is surrounded by a small portion of a coarsely granu- 

 lar mass. Often a distinct nuclear membrane is to be seen, and some- 

 times within it a highly refringent nucleolus ; more often, however, only 

 fragments of a nucleolus. They think it comes from the substance of 

 the disappearing germinative vesicle, either before or during fecundation. 

 It is applied to the inner surface of the watch-glass-shaped elevation of 

 the egg membrane,t but never at the highest point of the dome ; and 

 when the micropyle is eccentric, it is found on the side of the dome 

 opposite the latter. The authors combat the view entertained by Cal- 

 berla, that the germinative vesicle gives place to a female pronucleus 

 at the time of the metamorphosis of the " Ammocetes " into the adult. 

 " Aber diese Auffassung (Calberla's) verliert alien Boden durch den von 

 uns gef iihrten Nachw.eis, dass am Beginne des Befrucktungsactes ein Bich- 

 tungskorper eliminirt wird " (p. 20). The proof is not entirely satisfac- 

 tory to me, for I do not see what direct evidence has been produced to 

 show that the supposed polar corpuscle may not have been eliminated 

 from the yolk at a much earlier period than that of fecundation. That 

 it might after elimination become enveloped by the yolk, — which be- 

 fore fecundation fills completely the egg membrane, — and thereby 



* The signification of this " Dotterhiigel " and its relation to the first plane of 

 segmentation will be discussed hereafter. See p. 499. 



t See the account given elsewhere (p. 501) of the changes accompanying fertiliza- 

 tion. 



