524 MATURATION AND IMPREGNATION OF THE OVUM. 



accounts, so far as they go, have been given of the gradual 

 atrophy of the germinal vesicle. The description of Kleinenberg 

 (14) for Hydra, and Gbtte for Bombinator, may perhaps be 

 selected as especially complete in this respect ; in both instances 

 the germinal vesicle commences to atrophy at a relatively early 

 period. 



Coming to the more modern period the researches of five 

 workers, viz. Biitschli, E. van Beneden, Fol, Hertwig, and 

 Strasburger have especially thrown light upon this difficult sub- 

 ject. It is now hardly open to doubt that while part of the 

 germinal vesicle is concerned in the formation of the polar cell 

 or cells, when such are present, and is therefore ejected from the 

 ovum, part also remains in the ovum and forms a nuclear body 

 which will be spoken of as the female pronucletis, the fate of which 

 is recorded in the second part of this paper. The researches of 

 Biitschli and van Beneden have been especially instrumental in 

 demonstrating the relation between the polar bodies and the ger- 

 minal vesicle, and those of Hertwig and Fol, in shewing that part 

 of the germinal vesicle remained in the ovum. It must not, 

 however, be supposed that the results of these authors are fully 

 substantiated, or that all the questions connected with these 

 phenomena are settled. The statements we have are in many 

 points opposed and contradictory, and there is much that is still 

 very obscure. 



In the sequel an account is first given of the researches of the 

 above-named authors, followed by a statement of those results 

 which appear to me the most probable. 



The researches of van Beneden (3 and 4) were made on the 

 ovum of the rabbit and of Asterias, and from his observations 

 on both these widely separated forms he has been led to con- 

 clude that the germinal vesicle is either ejected or absorbed, 

 but that it has in no case a genetic connection with the first 

 segmentation sphere. He gives the following description of the 

 changes in the rabbit's ovum. The germinal vesicle is enclosed 

 by a membrane, and contains one main germinal spot, and a few 

 accessory ones, together with a granular material which he calls 

 nucleoplasma, which affects, as is usual in nuclei, a reticular 

 arrangement. The remaining space in the vesicle is filled by a 

 clear fluid. As the ovum approaches maturity the germinal 



