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THE AMERICAN NATURALIST 



[Vol. L 



division of the chromatin, as effected in karyokinesis is 

 indispensable as a preliminary to the production of iden- 

 tically-similar daughter-cells by division of a parent-cell. 

 Hence it becomes intelligible why, amongst Metazoa, we 

 find the occurrence of nuclear division by karyokinesis in 

 its most perfect form to be the rule, and "direct" division 

 of the nucleus to be the rare exception, while, on the other 

 hand, in the Protista, and especially in the Protozoa, we 

 hud every possible stage in the gradual evolution of the 

 exact partition of the chromatin in the process of nuclear 

 division, from chromidial fragmentation or the most 

 typical amitosis up to processes of karyokinesis as per- 

 fect as those of the Metazoa. 



There now remains only one point of general interest 

 in the evolution of the cell to which brief reference must 

 be made, namely, the divergence of animal and vegetable 

 cells. Not being a botanist, I desire to approach this 

 question with all caution; but as a protozoologist it seems 

 to me clearly indicated that the typical green plant-cell 

 took origin amongst the Flagellata, in that some members 

 of this group of Protozoa acquired the peculiar chromat- 

 ophores which enabled them to abandon the holozoic or 

 animal mode of life in exchange for a vegetative mode of 

 nutrition by means of chlorophyll-corpuscles. It is well 

 known that many of these creatures combine the posses- 

 sion of chlorophyll with an open, functional mouth and 

 digestive vacuoles, and can live either in the manner of 

 plants or of animals indifferently or as determined by 

 circumstances. It would be interesting to know exactly 



