246 WHITMAN. ' [Vol. I. 



portant point Fol's investigations leave us in the lurch ; for, 

 while he describes the cone (p. 91) as arising from the cortical 

 layer of hyaline protoplasm (which layer represents the vitelline 

 membrane ab initio Hertwig, in posterum Fol) he finds himself 

 unable, when he comes to a final discussion of the matter (pp. 

 250-251), to decide whether the cone forms a part of this layer 

 or a part of the vitellus proper. As there is no doubt ex- 

 pressed about the continuity of the cone with the vitellus after 

 the penetration of the spermatozoon, it may be safely inferred 

 that the continuity exists from the outset. 



If Fol's theory of the origin of the vitelline membrane were 

 correct, — it is difficult to accept it in the face of Hertwig's ob- 

 servations, which accord so much better with our general knowl- 

 edge of related phenomena, — the origin of the cone from the 

 cortical layer could easily be reconciled with its continuity with 

 the vitellus, since this entire layer is supposed to be an integral 

 portion of the &g% protoplasm up to the moment of impregna- 

 tion. The delimitation and separation from the vitellus, re- 

 sulting from impregnation, would take place all around the 

 cone, leaving the cone still continuous with the vitellus. This 

 view finds its strongest support in the fact that when several 

 spermatozoa enter the same q:^% at different points, as may 

 happen in pathological cases, a cone of attraction is developed 

 at each of these points (p. 119). 



Although any point of the egg may give rise to one of these 

 cones, it is still probable that, in all normal cases, the single 

 cone arises from a differentiated place, which corresponds to the 

 Dotterhiigel of Toxopneustes. When the cone is first seen, it 

 has the form of a low, " nipple-like prominence " (p. 91), like 

 the " Dotterhiigel " in the q^^ of the sea-urchin. 



Flemming states that this prominence is quite difficult to find 

 in T. lividus, and that it must be carefully searched for by 

 rolling the egg slowly, and examining attentively every point of 

 the surface. It is probable that Fol overlooked this prominence 

 until, at the penetration of the spermatozoon, its exact position 

 was marked and easily brought into the field of vision. 



The " Dotterhiigel " of Selenka, the " Hockerchen " of Flem- 

 ming, the " Protoplasmabriicke " of Hertwig (18, p. 173), and 

 the " c6ne d'attraction " of Fol are, in all probability, identical 

 in origin and function; and Selenka's observations on the 



