Hyatt] 65 [1884. 



simply introduces an element of specialization into the processes 

 of fusion. 



We also know from the researches of authors, that the division 

 of the nucleus almost invariably precedes the subdivision of 

 the cell, and that this is also the case among Protozoa. As a 

 preliminary to conjugation, however, we find that division of the 

 nucleus does take place, and also in multinucleated ceils, with- 

 out being necessarily followed by cell division, though it evi- 

 dently belongs to the segmental class of reproductive phenom- 

 ena. The probable causal connection here seems to be quite as 

 evident as is that between the segmentation or maritonucleus in 

 the egg and the subsequent self-division of that body. Thus we 

 are entirely at liberty to present the division of the nucleus 

 as a necessary preliminary to the still greater differentiation in 

 which the cell is male or female according to the preponder- 

 ance of one or the other of the two parts* of the nucleus. 

 That any sexual differences in the development of nuclei intro- 

 duced by change of habit or difference in food could be seized 

 upon by natural selection, and increased until cross fertilization 

 became a necessity, is almost an inevitable conclusion from what 

 we know of the bad effects of interbreeding among the higher 

 animals. 



The common accident of fusion between soft-bodied Amoe- 

 bae, and other Protozoa, would have been the first step lead- 

 ing to the adoption of fusion as an advantageous habit introduc- 

 tory to cross fertilization and resulting in greater reproductive 

 power on the part of the crossed individuals or zoons through 

 the inevitable blending of their nuclei. Any primitive differentia- 

 tion in a body like the nucleus, whose functions are generally 

 admitted to be essentially reproductive, would naturally be a 

 sexual distinction. The mere division of the nucleus would have 

 been the first step, the next steps must have been the acquisi- 

 tion of different habits, functions, and finally structure, by the 

 divided nuclei. One part of the divided nucleus would necessarily 

 tend to acquire reproductive habits distinct from the other part, 

 and the ultimate result of division into nuclei, however numer- 

 ous these might be at first, would be the production of only two 

 kinds, male and female. With this differentiation beoinningr 

 to be established between the different products of the nucleus, 



PROCEEDINGS B. S. N- H. VOL. XXIII. 5 JAJSUARY, 1885. 



