50 



BIOLOGICAL LECTURES. 



stain. But in the egg of AUolobophora foetida I have been 

 able, by two different methods, to differentiate the two struc- 

 tures. Staining substances differently is a relatively safe 

 method; but staining substances alike in order to prove their 

 identity is a very dangerous one. We all know numerous exam- 

 ples where this method proves to be a weapon which shoots 

 backwards and tempts us to assert relationships where they do 

 not exist. But we must not forget that even differential stain- 

 ing is not entirely trustworthy; for chromatin has been shown 

 to select different stains at two different stages of its develop- 

 ment, and yet we do not question its being chromatin at either 

 stage. I hope to be able to support the evidence of differential 

 staining by tracing the fate of the middle-piece after it enters 

 the Qg%. 



A careful, and I trust conscientious, study of the sperm 

 attraction sphere of the (tgg of AUolobophora foetida has led 

 me to the following conclusions: I believe that all its parts 

 (centrosome, archoplasm, and rays) are morphologically the 

 same substances as the corresponding parts of the egg attrac- 

 tion sphere, and that each one of these parts is merely an 

 aggregation of a substance existing throughout the cytoplasm 

 (Figs. 2, 3, 4). I believe that the sperm attraction sphere is a 

 cytoplasmic phenomenon just as much as the fertilization cone 

 is a cytoplasmic phenomenon (Figs. 2, 3). Why cannot the 

 sperm attraction sphere be an expression of a definite effect 

 produced upon the cytoplasm by the entrance of the sperm, 

 just as the fertilization cone is a cytoplasmic phenomenon 

 which does not appear until the sperm enters the ^g^ ? 



Let me compare the two phenomena, the fertilization cone 

 and the sperm attraction sphere. In this egg both structures 

 appear to depend not alone upon the entrance of the spermato- 

 zoon, but also upon a definite stage of development reached by 

 the egg; the cone is never found after the first polar body is 

 constricted off,^ and the sperm attraction sphere is never found 



1 After examination of nearly one thousand eggs, I have found only a few in 

 which the head of the spermatozoon is penetrating the egg after the first polar 

 body is formed, and in none of these cases have I found a cone ; but it is possible 

 that the cytoplasm of these eggs may not be entirely normal, though it appears to 



