586 BULLETIN OF THE 



the former, sucli as must result if such a filament exists, it only remains to 

 assume pre-existing filaments which arise from the surface of the vitellus. 

 These might, a 'priori, be represented as extremely delicatt? filaments traversing 

 the oolema in radial lines ; but as they have never been discovered in the 

 hardened or living egg, it is necessary to deny their existence. The second 

 hypothesis is that the action of the vitellus is in response to a pressure exerted 

 by the zoosperm upon the intervening portion of the striate envelope through 

 which it endeavors to advance. As the vitellus does not react upon the press- 

 ure of all kinds of bodies, it is necessary to admit that there is some peculiar- 

 ity, — some special rhythm arising from the undulations of its cue. But it is 

 difficult to understand how this pressure could be appreciated through half the 

 .thickness of the oolema, or communicated to a definite extent of the vitelline 

 surface, or why the cone of attraction should arise exactly opposite the most 

 advanced zodsperm. The last supposition consists in admitting an attraction, 

 the nature of which is unknown, which exercises an influence not only by im- 

 mediate contact, but also at a slight distance ; although this hypothesis itself 

 needs to be explained. The composition of the cone of attraction is not better 

 understood. Is it a substance secreted by the vitellus, or a prolongation of the 

 vitelline sarcode, and, in the latter case, is it an accumulation of the superficial 

 limiting layer, or of the deeper layer 1 The first hypothesis is excluded, in the 

 author's opinion, by the case where the protuberance is of considerable volume, 

 and the continuity of its substance with the vitelline sarcode is evident, but 

 between the other two hypotheses he remains undecided. The cone of exu- 

 dation, on the other hand, is only a liquid, slightly refringent substance, 

 without cohesion, which is ejected or excreted by the surface of the yolk. 



Fol distinguishes three kinds of centres of attraction, — the male, the female, 

 and those which preside at segmentation. The male centre takes its origin in 

 a spermatozoon,* whose " hody " becomes the centre of an aster and the point of 

 departure in the formation of the male pronucleus. I am not certain what 

 he means by that part of the statement which I have italicized, since he has 

 shown more clearly than any one else that the male aster does not always 

 centre at the middle of the male pronucleus. I can reconcile this statement 

 with the fact mentioned only by assuming, either that he thinks the male pro- 

 nucleus is formed eccentrically to the head of the spermatozoon, or that this 

 statement is only intended to be an approximate expression of facts. The 

 former assumption is the less probable, because he adds : " It is important not 

 to forget that the body of the spermatozoon is no longer intact at the moment 

 when these phenomena (astral) appear ; it has changed form and has in- 

 creased in size by the absorption of vitelline sarcode." I therefore think the 



* The author thinks recent observations tend to show that the spermatozoon is 

 formed of cellular protoplasm, to the exclusion of the substance of the nucleus. Conse- 

 quently the male pronucleus is formed by the union of two protoplasms, which have 

 not suffered a single admixture of the substance of preformed nuclei. ** Le pronu- 

 cleus male ne descend \ acun titre, pas meme en partie, d'un noyau plus ancien ; il 

 est de formation nouvelle." 



