No. 2.] OOKINESIS. 247 



behavior of the spermatozoa towards the " Dotterhiigel " go 

 to show that it is really a " bouchon d'impregnation." Selenka's 

 interpretation of this as a protuberance caused by the extrusion 

 of the polar globules is entirely unsupported by analogy in 

 other eggs; and, besides, it offers no explanation of the decided 

 preference shown by the spermatozoa for entering the &^^ at 

 this point. This preference must mean that the attraction 

 between the &^'g and the spermatozoon is strongest at the 

 " Dotterhiigel." Selenka accounts for it by supposing that the 

 gelatinous envelope of the &gg is more easily pierced in the 

 immediate vicinity of the Dotterhiigel than elsewhere. 



The fact that spermatozoa generally penetrate the envelope 

 vis-a-vis the " Dotterhiigel " may be quite as readily explained 

 on the hypothesis of attraction ; and this view is supported by 

 analogy, as we shall presently see, and by one of Selenka's own 

 observations. In case the spermatozoon passes through the 

 mucous envelope at some point more or less remote from the 

 " Dotterhiigel," it does not continue to advance straight through 

 the vitelline membrane (" Rindenschicht "), but " .yz^/m^ about 

 over the membrane for from one-Jialf to several minutes, until, 

 by its whip-like movement, it accidentally strikes its head against 

 the Dotterhilgcr' (p. 6). It then bores its way through the 

 membrane into the vitellus. 



The careful investigations of Zacharias have led him to con- 

 clude that there is no predetermined point of impregnation in 

 the egg of Ascaris. According to this author, the spermat- 

 ozoon penetrates at any point of the surface of the egg, and 

 Van Beneden's statements as to the existence of a micropylar 

 orifice are represented as entirely incorrect. " It is very remark- 

 able, however," says Zacharias (10, p. 143), "that in the great 

 majority of cases only a single spermatozoon copulates with 

 the egg of Ascaris. If no predetermined point of impregnation 

 is present, it is wJiolly inexplicable that only one of the many 

 hundred spermatozoa which surround the egg in the upper part 

 of the litems should become attached to it." The idea that the 

 receptivity of the egg is self-regulating does not seem to have 

 occurred to Zacharias. 



A very striking and convincing proof of attraction at a dis- 

 tance, and at the same time a confirmation of the interpretation 

 above given to Selenka's observations, is found in the fecunda- 



