No. 2.] OOKINESIS. 245 



tance. We believe that such attraction is exerted, not only by 

 the spermatozoon, but also by the &%g, and that the part it 

 plays in bringing together the sexual cells is no less important 

 than that taken by the tail of the spermatozoon. It is highly 

 probable, also, that tliis attraction is polar, and that the place of 

 penetration is a predetenni^ted point or region. 



On this question, however, we have conflicting testimony, 

 which has been considered at some length by Van Beneden 

 (9> PP- 371-376)- Fol and Hertwig concur in the opinion 

 that the spermatozoon may penetrate at any point; while 

 Selenka (7, p. 6) holds that, as a rule, it enters a preformed 

 protuberance of tJie vitellus (" Dotterhiigel"), but adds that in 

 about a dozen cases out of a hundred, it may effect an entrance 

 at any other point. Van Beneden suggests that this " Dotter- 

 hiigel " of Toxopneicstes variegatus (Selenka), and of T. lividus 

 (Flemming, 23), corresponds to the "bouchon d'impregnation " 

 in Ascaris; and this view appears to be well taken. It is sup- 

 ported by one very important consideration, not mentioned by 

 Van Beneden. I refer to the evidence of a micropyle, or micro- 

 pylar region, which may be drawn from the observations of 

 Hertwig, Fol, and Selenka. Hertwig (18, p. 173) has demon- 

 strated clearly that the vitelline membrane is present before the 

 copulation of the sexual products, and Fol (6, p. 94) has ob- 

 tained equally positive evidence of a small opening (" micropyle 

 d'occasion ") located in a crater-like inflection of this membrane. 

 Fol did not, however, recognize any such crater before the 

 spermatozoon entered the vitellus, but he did find the " cone 

 of attraction" before this event, and observed that the cone 

 remained in continuity with the vitellus " a travers la mem- 

 brane^' after the penetration of the spermatozoon. Allowing, 

 then, that both the cone and the membrane exist prior to 

 fecundation, the same must be conceded for the micropyle. 

 Only one way of avoiding this conclusion occurs to me. The 

 cone might be regarded as a portion of the membrane which 

 is thrown into continuity with the vitellus secondarily, as the 

 result of the penetration of the male element. There is an 

 obvious objection, however, to considering the " cone of attrac- 

 tion " as a part of the vitelline membrane. On this very im- 



23. W. Flemming. Beitrage z. Kenntniss d. Zelle u. ihrer Lebenserscheinungen. 

 Arch.f. mik. Anat., XX., 1882. 



