74 PROBLEMS OF FERTILIZATION 



nucleus within the same body of cytoplasm we must 

 attribute this either to the presence of some specific 

 substance originally present with the former, but not 

 with the latter, or to some other differential organi- 

 zation of the substances of the nuclei concerned. Boveri 

 took the former alternative and formulated it in terms 

 of a morphological theory of cell division. He thus 

 brought under one point of view the origin and locali- 

 zation of the sperm aster and the phenomena of cell 

 division, so that the theory of fertilization became part 

 of a theory of cell division. He stressed cell division 

 as the fundamental factor of development and over- 

 looked the more immediate and essential result of 

 activation of metabolism. 



The centrosome theory of cell division has not, 

 however, maintained itself in the face of advancing 

 knowledge of cell morphology and physiology. Boveri's 

 theory of fertilization would thus lose much of its sig- 

 nificance even if it were demonstrated that the sperm 

 centrosome is a derivative of the spermatid centrosome, 

 and this is far from being the case. Not only is there 

 a hiatus in the history, but the experiments on Nereis 

 previously cited show that the sperm nucleus itself 

 contains material for inciting formation of a sperm 

 aster and its centrosome. It is possible to attribute 

 this to specific centrosome material contained within 

 the nucleus, if the centrosome theory of cell division 

 is adhered to, but it is also possible to explain it in a 

 more physiological manner to be considered hereafter 

 (p. 265). A finer morphological analysis is no doubt 

 possible and will be useful, but we must recognize the 

 'fact that in fertilization we are dealing with a physio- 



