542 BULLETIN OF THE 



by Whitman (his "nucleoplasm") and others point in the same di- 

 rection. 



0. Hertwig has shown experimentally in the starfish, that, when fecun- 

 dation is introduced before the formation of the female pronucleus, the 

 male pronucleus attains the same dimensions as the female ; but when 

 fecundation is delayed until after the female pronucleus is developed, it 

 remains much smaller than the latter. The explanation implied in 

 Hertwig's statements is, that in the latter case the female pronucleus 

 has already appropriated, as it were, the lohole of the available nuclear 

 fluid. The same theory Hertwig thinks valid in explaining constant dif- 

 ferences in the relative sizes of the pronuclei after normal fecundation in 

 different animals. Thus in Toxopneustes, where the events of matura- 

 tion transpire before fecundation, the male pronucleus remains small, 

 while in mollusks, etc., spermatization having been effected before these 

 events, the two pronuclear bodies attain the same size. In so far, then, 

 as this theory serves to explain phenomena, it establishes its claim to 

 acceptance. But there exist certain objections to this view. It seems 

 to necessitate the belief in a fixed amount of unengaged nuclear fluid, 

 which, I believe it is fair to assume, the author must identify with that 

 which was liberated at the metamorphosis of the germinative vesicle. 

 That being the case, the theory necessitates the uniform diffusion of this 

 liberated fluid through the whole yolk ; as, otherwise, how could a male 

 pronucleus, arising indifferently at any point near the surface, enjoy the 

 same opportunity for the acquisition of it as a female pronucleus origi- 

 nating in the immediate vicinity of the place where it was set freel 

 Although the male pronucleus has been seen before the formation of the 

 first polar cell, it does not appear that it increases much in size, or is far 

 removed from the surface of the yolk, before the production of the second 

 polar cell ; that is, before the time the substance of the female pro- 

 nucleus loses its connection with the substance of the last polar cell. 

 It then exhibits a more or less rapid growth and migration. But if it 

 is simply dependent for its increase iai size on the liberation of nuclear 

 fluid, I see no reason why it should not greatly increase, even before the 

 production of the first polar cell, in cases where the spermatization is 

 effected before the events of maturation. And if Hertwig's reasoning 

 is correct, why should it not, in these instances of early fertilization, 

 acquire the major portion of the available nuclear fluid, and thus sur- 

 pass in size the female pronucleus, instead of simply reaching an equal- 

 ity with it % May it not be that differences in the growth of the male 

 pronucleus are explainable without recourse to the supposition of a fixed 



