Ryder.] 126 [May 16, 



are diverted into another channel ending in the metabolism of both indi- 

 viduals manifesting itself in the production of a larger amount of fresh 

 chromatin, capable of taking upon itself the work of the former nucleus, 

 a part being pushed or "set aside " as a functionless surplus ready to be 

 stimulated to growth through conjugation. Maupas' theory of senescence 

 may therefore be regarded as in the highest degree probable, in that in 

 those cases where conjugation has long been in abeyance the stimulus of 

 growth leading to the production of an abundance of chromatin has been 

 absent. From this point of view the Infusoria present a most specialized 

 type of reproductive activity in which the cytoplasm and chromatin have 

 never been freed or separated from each other as marking independent 

 sexual states in which these two cellular constituents have preponderated, 

 as the female and male respectively. In other words, the Infusoria are 

 practically oosperms which are reciprocally stimulated to reproductive 

 activity through the act of conjugation. 



The ovum of the Metazoa is in the same case with the Infusoria, but 

 behaves differently because it is purely an ovum. Here the polar bodies 

 are to be regarded as exhausted chromatin or nucleoplasm with a decidedly 

 male tendency in that the cytoplasm investing them is usually small in 

 amount. The polar bodies are to be regarded as representing not only the 

 disintegrated macronucleus but also the disintegrated fragments of the 

 first or preparatory stages of division of the micronucleus. While the 

 products of the fusion of the pronuclei of Infusoria again contrast with 

 the fusion products of the pronuclei of Metazoa, in that they are at once 

 divided into a functional or physiological and a functionless or reproduc- 

 tive nucleus. In the Metazoa the separation of reproductive functions 

 from the other physiological ones is effected through cell-division and 

 does not coexist in two nuclei lying side by side in the cytoplasm of the 

 same cell. 



Nevertheless, there is reason to believe that the chromatin of the egg 

 is partly exhausted, as it is in the Infusoria, and must be got rid of in part 

 in order to regenerate the remaining chromatin through a process of 

 growth accompanied by active karyokineses. This exhaustion supervenes 

 upon the prolonged exercise of its physiological function in building up a 

 large amount of investing cytoplasm under conditions which have inter- 

 fered with the normal segmentation of the whole into cells no larger than 

 those of the rest of the body. The characteristic overgrowth of the ovum 

 beyond the size of its companions in the body of a Metazoan, is the real 

 ground of the specialization of the egg through which it may be supposed 

 that part of its nuclear matter has been exhausted through prolonged ex- 

 ercise of the physiological functions of the nucleus. It will be seen that 

 this view is similar to that of Weismann, but it is more specific. Accord- 

 ingly the degree of specialization of an ovum must influence the extent 

 to which its nucleus is exhausted. Parthenogenetic ova are for obvious 

 reasons to be regarded as less specialized than those which are not par- 

 thenogenetic. This hypothesis therefore fits in well with the fact of the 



