176 EDOUARD VAN BENEDEN. 



Echinoderm the germinal spot passes out of the germinal 

 vesicle, and becomes free in the vitellus, and there forms 

 the nucleus of the yolk. But if 1 may judge from the 

 figures which he gives of the germinal vesicle in process of 

 retrogressive metamorphosis, I am convinced that the spot 

 of Waguer in that Echinoderm undergoes the same fragmen- 

 tation which I have mentioned in the starfish. I believe 

 that the germinal bodies which M. Hertwig figures in the 

 germinal vesicle (figs. 3, 4, 5, and 6) are nothing but the 

 fragments of the nucleolar substance. It may be remarked 

 that in his work M. Hertwig gives no information on the 

 subject of these granules : he does not describe the pheno- 

 mena which relate to the progressive metamorphosis of the 

 vesicle; he confines himself to saying: "At the time of 

 maturity of the egg, the germinal vesicle undergoes retro- 

 grade metamorphosis, and is driven by contraction of the 

 protoplasm to the surface of the yolk. Its membrane is 

 dissolved, its contents liquefy, and are finally absorbed by 

 the yolk; the germinal spot, however, appears to remain 

 unchanged, to penetrate into the yolk-mass, and to become 

 the permanent nucleus of the ripe fertilizable egg-"^ 



Of all the observations published up to the present time 

 relating to the history of the germinal vesicle, the only ones 

 which present any analogy with those which I have made on 

 the starfish are those of Kleinenberg, on the fresh-water 

 Hydra." Kleinenberg, in fact, recognised that in that animal 

 the germinal spot of the mature ovum undergoes a retrogres- 

 sive metamorphosis ; it presents an irregular and angular 

 contour ; then it breaks up into little fragments, and these at 

 last dissolve. So far as concerns the spot of Wagner, the 

 description of Kleinenberg is as applicable to the Star- 

 fish as to the Hydra. As to the description which he 

 gives of the mode of disappearance of the germinal vesicle, 

 it difiers very notably from what I have seen in the Star- 

 fish. But at the end of his description Kleinenberg says : 

 ''Once I thought I saw an actual hole in the membrane of 

 the germinal vesicle. If this is a normal phenomenon, it 

 would be possible for the contents of the vesicle to escape 

 and mingle with the surrounding plasma." I believe that 

 the formation of the hole which Kleinenberg believed he 

 saw is a normal phenomenon, and that it is by the formation 

 of this hole that the contents of the vesicle are partially 

 eliminated, both in the Hydra and in the Starfish ; and it 

 is as a result of the rupture of the membrane that the 



* O. Hertwie^, loc cit., pages 11 and 12. 

 ' Kleinenberg, Hydra, page 24. 



