250 C. O. WHITMAN. 



mammalian ovum. Tlie object of study (egg of rabbit) was 

 much more difficult to follow than those selected by Hertwig, 

 but the same conclusion was reached in regard to the sexual 

 character of the pronuclei, although not in regard to the exact 

 origin of the same. These points of difference have been dis- 

 cussed at length by van Benedeii (16, 1870), and so far as tiiey 

 concern the structure of the male pronucleus, have already beeu 

 noticed. 



According to the latest paper on this subject by Hertwig 

 (a-yT'V'Tr) t'he female pronucleus rej)rescnts that half of the 

 amphiaster that remains after the formation of the last polar 

 globule. 



On the other hand, van Beneden (tW) believes that there is 

 no " genetic connection between the germinal vesicle, or one of 

 its parts, and the embryonic nucleus " (cleavage-nucleus). I 

 have already shown that this opinion is entirely incompatible 

 with what takes place in the egg of Clepsine, and it is evidently 

 untenable in view of the researches of Eol. I shall venture to 

 point out what seems to me an inconsequence in van Beneden's 

 statements, which, as I think, makes it quite unnecessary to 

 accept his conclusion on this point. He affirms (tVt) ^^^^ in the 

 rabbit a part of the germinal vesicle, the nuclear fluid (" liquid 

 clair '■*) remains in the egg after the expulsion of the polar 

 globules, and becomes " confounded with the cortical substance 

 of the ovum, which from this moment is no longer dis^tinguish- 

 able from the medullary substance." All this happens before 

 fecundation ('-/). Soon after fecundation two pronuclei are 

 found, one of M'hich (" peripheral pronucleus ") arises in the 

 suj)erficial layer, and the other (" central pronucleus ") in the 

 central layer of the vitellus. 



How then is it possible to know that neither of these pro- 

 nuclear bodies contains any of the " liquid clair " that was con- 

 founded with the vitellus? If this is not known, then the 

 possibility of a genetic relation between the germinal vesicle and 

 the cleavage-nucleus, which is the product of a coalescence of 

 the two pronuclei, still remains. Is this possibility deni(d 

 because the nuclear fluid mixed with the proto))lasm of the 

 ovum? How then in the case of the starfish (tSV) can Van 

 Beneden believe that the polar globules have the same origin as 

 in the rabbit? Tt is asserted positively that everii part of the 

 germinal vesicle (staifish) dissolves and becomes diffused through 

 the vitellus ; and yet van Beneden does not hesitate to say — 

 " yince in the starfish directive bodies are eliminated by the yolk, 

 it is probable that in the Echinodcrmata, as in Miunmalia, these 

 bodies are formed by the nucleoplastic substance on the one 

 hand, and by the nucleolar matter, joined to the substance of 



