410 



authors, building on the first set of facts, have declared that 

 the germinal vesicle and sjoot are very important for the first 

 stages of egg growth, but that at the period when the egg is 

 ready for fertilisation their function is ended, and they are no 

 more wanted. Others, again, with equal force, pointing to the 

 latter set of facts, declare that the germinal vesicle by its 

 division furnishes the nuclei of the first embryonic cells, and 

 would regard the disappearance as only apparent in the first 

 cases, since a pair of nuclei exactly like the divided germinal 

 vesicle a]3pear immediately after the first cleft is complete in 

 all those cases where the germinal vesicle is found to^be want- 

 ing at the time of fertilisation. 



Dr. Van Beneden lays some stress on this, as well as on 

 the fact that in some observations of his on rabbits, he found 

 a sort of irregularity in the perceptibility or apparent absence 

 of nuclei in the two first cells, due to yelk cleavage. Thus, 

 in one case observed two hours after copulation, the yelk was 

 found cleft into two cells, each with a nucleus, although at 

 the time of fertilization it is not possible to observe a ger- 

 minal vesicle. In another case, on the contrary, twenty-four 

 hours after copulation, he found the two cells but no nucleus 

 in either. He has also fully established the same sudden 

 disappearance of the nuclei in the cells of the 3rd or 4th gene- 

 ration, reappearing as in the first cleavage, after the process. 

 He also confirms Weismanm's observation of the similar 

 disappearance of the nuclei in the cells of the blastoderm of 

 dipterous insects when they were about to undergo division. 

 He also makes a point, in observing that if the nucleus or 

 germinal vesicle did really break up and perish, there would 

 not suddenly aj)pear in each half of the divided mass, a 

 nucleus equal in size to the bulk of the lost vesicle; if new nuclei 

 were produced by endogenous formation, they would form by 

 degrees, and as small points at first, and would not suddenly 

 jump into existence fully grown. Dr. Van Beneden belongs 

 to that party which w^ould regard the disai^pearance of the 

 germinal vesicle in the case of Mammifers, Birds, Batrachia, 

 Annelids, &c., as apparent rather than real. "We are quite of 

 his opinion here, and in any case would hesitate to accept the 

 assertion of the death of the germinal vesicle before fertilisa- 

 tion. The host of cases in which its active life has been 

 clearly traced as the original nucleus of the embryo-cells 

 demands some other explanation than this. On this ground, 

 we wonder that Mr. Hutchinson Stirling in an essay on 

 Protoplasm, which is, if we may say it, overladen with 

 references to the knowledge and wisdom of the Germans — 

 the author accepting all that is presented to him in German 



