EMBRYOLGY OF CLEPSINE. 247 



ovum of the rabbit have proved to me that no morphological 

 part ot the germinal vesicle is found in the yolk at the moment 

 of fecundation. The nucleolus united with the substance, which 

 constituted the membrane of the vesicle, is eliminated to form 

 one of the directive bodies; the nucleoplasma with the pseudo- 

 nucleoli are thrown off into the perivitelline liquid, to form there 

 the second polar globule. The liquid of the vesicle remains in 

 the yolk, and becomes confounded with the cortical substance of 

 the ovum, which from this moment is no longer distinguishable 

 from the medullary substance. There can not then be, in the 

 rabbit, any genetic connection between the germinal vesicle or 

 one of its parts, and the embryonic nucleus, which appears in the 

 egg after fecundation (tS't)j starfish). The successive pheno- 

 mena which precede the complete disappearance of the germinal 

 vesicle are these: — 1. The solution of the nucleoplasmic mass 

 and of the pseudo-nucleoli in the nuclear juice; 2. The breaking 

 up of the germinal spot into fragments, and the progressive 

 solution of these fragments in the nuclear substance; 3. The 

 perforation of the membrane, followed by the partial expulsion 

 of the contents of the nucleus ; 4. The complete solution of the 

 membrane in the juice of the germinal vesicle; 5, lastly, the 

 solution of the nuclear substance in the vitelline protoplasm.'^ 

 Are the results arrived at by van Beneden, accurate as they un- 

 doubtedly are in most respects, decisive on the point in question? 

 It is asserted with positiveness that the germinal vesicle dis- 

 appears, and that polar globules arise in both cases, but there is 

 a striking difference in the manner of disappearance. 



In the rabbit, the nucleolus, nucleoplasm, and membrane are 

 eliuiinated as two polar globules, the nuclear fluid alone remain- 

 ing and mixing with the vitelline mass ; while, in the starfish, 

 all these elements are dissolved and confounded with the proto- 

 plasm of the egg, no genetic relation being found between them, 

 or any part of them, and the polar globules. It is this failure to 

 bring the polar globules into connection with the germinal 

 vesicle, that shows conclusively that van Beneden's results are, 

 in this case at least, undecisive. The egg of the starfish is by 

 far more favourable for the study of these phenomena than that 

 of the rabbit, for the successive phases can here be brought under 

 direct and continued observation, while in the rabbit this is 

 impossible. We caimot, then, accept the results in either case 

 as decisive. Had van Beneden supplemented his observations 

 on the living egg, by the use of re-agents, at the moment of the 

 supposed disapj)earaHce of the germinal vesicle, as Hertwig and 

 Fol have recently done, he would undoubtedly have arrived at a 

 very difterent conclusion. 



It would be difficult to prove that the germinal vesicle 



VOL. XVIII. NEW SKK. R 



