248 C. O. WHITMAN. 



becomes neither physiolopcally nor mnrpliologically extinct, 

 more conclusively than lias been done by the last two-mentioned 

 authors, liotli have followed these changes repeatedly in the 

 living egg, and both have confirmed what they saw in this way 

 by the examination of corresponding stages treated with re-agents. 

 Both have arrived at essentially the same conclusions, differing 

 only in regard to the role played by the nucleolus. The conclu- 

 sion reached in each case is, that the polar globules and the 

 female pronucleus are products of the germinal vesicle. 



The investigations of Blitschli (ttj^, Neritina fluviatilis) cor- 

 roborate all this, and are all the more convincing as they compel 

 Biitschli to abandon the opinion previously expressed (-^VV)? 

 that the entire germinal vesicle is expelled in the form of polar 

 globules, and to accept the view maintained by Hertwig — 

 namely, that the polar globules are composed not only of nuclear 

 substance, but also of protoplasm, and that a part of the ger- 

 minal vesicle remains in the egg, as a nuclear element, after pro- 

 ducing the polar globules. 



A similar case of confirmation is found in Strasburger's expe- 

 rience with Phallusia mamillata (^^l^)- Strasburger found, upon 

 a second examination, by usiijg osmic acid and carmine, that the 

 germinal vesicle had not wholly disappeared, as he at first 

 supposed, and sums up his conclusion thus : " Aus alien diesen 

 Betrachtungen scheint mir hervorzugehen, dass ein T/ieil des 

 alten Keimhldachens sfefs im thierlsclien Ei verbleibf.'" The 

 results attained by these authors appear to me to be decisive 

 against the oi)inion that every part of the germinal vesicle is 

 extruded in the form of polar globules, or completely confounded 

 with the vitelline protoplasm. 



So far as Clepsine is concerned, it is not of course possible to 

 prove by direct observation that the archiamphiaster is a product 

 of the germinal vesicle; but if this point be admitted — and 

 there seems no longer any room for doubling it — tiien it is 

 perfectly clear that a part of the germinal vesicle remains jxr- 

 manently in the egg. Plate III, fig. 63, proves that half of the 

 amphiaster which produced the second polar globule, remains in 

 the egg. This remaining half is seen as a pellucid spot in the 

 living egg, and on sections as a clear, round body, composed of 

 nuclear substance, and containing two nucleoli. I consider 

 therefore that in Clepsine the proof is as complete as it can well 

 be for o])aque iggs, that a part of ihe germinal vesicle persists as 

 a nuclear claiioit. 



{h) Pronuclei (Van Benedcn) and Cleavage-nucleus (Hertwig). 

 The cleavage-nucleus, om; or the other pronucleus, and pro- 

 nueleoli, have been seen at diUcrcnt times in the j)ast ; but tiieir 



