506 BULLETIN OF THE 



and are closely applied to each other. They are still sharply outlined, 

 but only slightly stained with carmine. 



The cleavage nucleus becomes more elongate, and, to judge from his 

 Fig. 71, more sharply defined; but the pronucleoli do not become fused 

 until the ^'nucleus" [central area] has assumed the spindle shape, nor even 

 until the first cleavage spindle begins to form. Whitman, it is true, does 

 not figure any stage in which the bodies in question remain intact 

 after the cleavage spindle begins to appear ; but I wish to call attention 

 to the fact that he says (p. 24) such is the case, for it seems to me an 

 important point in helping to prove the identity between the structures 

 which Whitman calls pronucleoli and those which I have called the pro- 

 nuclei. I do not understand how this late coalescence of the bodies in 

 question corroborates the view that they are nucleoli rather than nuclei. 

 I can see a priori no reason why either a dissolution or a coalescence of 

 nucleolar structures should be delayed beyond the time when a like fate 

 overtakes the nuclei ; on the contrary, evidence is not wanting that in 

 the metamorphosis of the germinative vesicle, where there will be no 

 ground for disagreement as to the nuclear nature of the vesicle, the 

 nucleolar elements are often the first to undergo radical change. Out 

 of numerous cases I will cite only 0. Hertwig ('77", pp. 277, 278) for 

 Pterotrachea. The case of the germinal vesicle, it is true, is not one 

 in which we have to do with the fusion of similar elements, yet when 

 we consider that the metamorphosis in both cases is one which leads 

 directly to the formation of the spindle, I think the justice of the com- 

 parison will not be denied. In Whitman's opinion, " the size, structure, 

 chemical behavior, and destiny of these bodies " favor his interpretation. 



It is of course important to ascertain at first if the bodies in question 

 are really the same in the case of Clepsine and Limax. There appears 

 little or no room to doubt this identity, notwithstanding their rather 

 striking differences of size, since, on the one hand. Whitman identifies 

 respectively his pronucleus and pronucleolus with the " Strahlensys- 

 teme " * and the minute corpuscles embraced in the same, as described 

 for Nephelis by Biitschli and Hertwig ; and since, on the other hand, the 

 questionable structure in Limax, though ultimately far from minute, 



* To assume that the radial systems are the nuclear structures (the pronuclei in 

 this case) seems to lead one into the unfortunate position of being compelled to 

 identify the whole, or nearly the whole, protoplasm with the nucleus, for the radial 

 systems at one time or another stretch through the entire yolk ; therefore I have 

 come to the conclusion, which is supported by what is said elsewhere (Whitman, 

 pp. 21, 25), that the author means to designate only the clear central areas of the 

 radial systems as nuclear structures. 



