266 PROBLEMS OF FERTILIZATION 



The karyokinetic phenomena thus initiated tend to 

 occupy the entire egg, but they are in conflict with the 

 maturation divisions when these have not already 

 occurred, and their extension is in such cases delayed. 

 But after this conflict has disappeared the extension is 

 very rapid. The meeting of the germ nuclei, as previ- 

 ously argued (p. 65), is due to their relation to the 

 single dynamic system of the entire egg, in which they 

 tend toward the center according to the universal rule 

 governing nucleocytoplasmic localization. There is no 

 reason for assuming any such vague, semimystical con- 

 ception as a "sexual affinity" of the germ nuclei. 



Many of the phenomena concerned in the internal 

 events of fertilization or artificial activation are of a 

 general cytological kind; the writer has therefore not 

 seen fit to discuss them, as this is not a treatise on gen- 

 eral cytology. We have attempted to isolate from the 

 complex of events those which are peculiar to fertili- 

 zation as such and to indicate their relations to known 

 physiological processes. 



3. General. As will have been seen from the preced- 

 ing discussion most of the theories of fertilization are 

 activation theories alone. Boveri's theory of the cen- 

 trosome, though entirely morphological, is such a 

 theory; such also are the various theories of Loeb, 

 R. S. Lillie, Delage, and others who have used arti- 

 ficial parthenogenesis as a means of analysis. On the 

 other hand, certain older theories, such as that of Oskar 

 Hertwig, take cognizance mainly of the problem of 

 biparental inheritance presented by fertilization. There 

 is obviously need for a theory that shall comprise the 

 main fundamental features of the fertilization reaction, 



