ON CARYOKINESIS. 1/3 



instance, as my friend Dr. C. Ishikawa tells me, the 

 summer and winter eggs of a certain species of DapJinia 

 undergo different '' types " of cleavage, one being holo- 

 blastic and the other being meroblastic, the difference 

 being produced probably by the conditions of the 

 cytoplasm and its deutoplasmic contents. The same 

 may be said in regard to the cleavages in different 

 species of Peripatits^ as the studies of Sedgwick and 

 others have shown. The same is true in the case of 

 Renilla as was shown by Wilson. In short, if we 

 classify animals by the "types" of cleavage or dif- 

 ferences of cleavage, rather than with reference to the 

 potential qualities of the nuclear substance, we fall into 

 an error of placing nearly related species of organisms 

 in different categories, nay, we even fall into the ab- 

 surdity of separating the individuals of one and the 

 same species into different groups. 



That the argument based on the arrangement of 

 superficial furrows alone is not entitled to any weight, is 

 further shown by their total absence in several forms of 

 ova, which nevertheless develop into perfect organisms. 

 It has been shown that in a certain plant, the cytoplasm 

 becomes divided without a corresponding division of its 

 nucleus. Such facts seem to point to the conclusion 

 that the division of the cytoplasm and that of the 

 nucleus are two independent phenomena, and that one 

 process can occur without the other, and that when they 

 do occur in close succession, as in ordinary cell-division, 

 it is to be looked upon as a case of coincidence. At any 

 rate, the following conclusion seems to be a valid one, 

 viz. that the division of the nucleus and that of the 

 cytoplasm are due to different causes. 



