250 whitman: ' [Vol. I. 



to the "bouchon d'impregnation " in Ascaris. Kupffer and 

 Benecke deny that the " Leitband " has the functional impor- 

 tance attributed to it by Calberla, and hence they prefer to call 

 it an " Axenstrang." ^ Allowing that it serves to guide the 

 spermatozoon into the vitellus, as asserted by Calberla, it is 

 difficult to see how it furnishes any evidence of attraction at a 

 distance. It is simply one of many protoplasmic threads, left 

 by the contractio7i of the vitellus, not a cone of attraction rising 

 from the vitellus to meet the spermatozoon. Neither the 

 observations of Calberla nor those of Kupffer and Benecke 

 permit us to identify the " Leitband" with the " bouchon" in 

 Ascaris. This "bouchon"^ arises before impregnation and 

 quite independently of any spermatic influences, while the Leit- 

 band arises merely as a secondary result of the action of the 

 spermatozoa. In view of the fact brought out by Kupffer and 

 Benecke, that the spermatozoa may penetrate at any point of 

 the micropylar area (" watch-glass"), and follow any one of 

 the protoplasmic filaments formed in this region, or even pass 

 between them in order to reach the vitellus, we would suggest 

 that the " bouchon" — if such a structure is present in the Lam- 

 prey egg — is represented by the discoid thickening (A. Mlil- 

 ler's " Deckel des Urblaschens ") of the thin protoplasmic 

 mantle. This disc occupies the active pole, and in extent cor- 

 responds closely with the micropylar area. (Cf. Kupffer and 

 Benecke's Fig. 7.) 



Nothing has yet been described in the teleostean Q.g^ that 

 could with certainty be said to function as a " cone of attrac- 

 tion." The observations which I have made on pelagic fish eggs 

 in conjunction with Mr. Agassiz are soon to be published else- 

 where, and I will not here anticipate the results further than to 

 say that a careful study of surface-preparations and sections 

 has revealed not the slightest trace of such a cone. I may 

 say, however, that conclusive evidence has been found that the 

 area of impregnation is, as might have been predicted from the 

 existence of a definitely localized micropyle, a limited one, 

 with boundary lines encircling the germinal pole. It is per- 



' The Axenstrang is not constant in Petronyzon fluviatilis (Kupffer and Benecke, 

 p. 18). 



^ There is no such structure according to Zacharias. 



