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THE AMERICAN NATURALIST [Vol. L 



methods of investigating both the functions and behavior 

 of the organism and of its parts. 



So long as eytologists limit their studies to the cells 

 building up the tissues of the higher animals and plants, 

 the comparative method has a correspondingly limited 

 scope, and that of the ontogenetic method is even more 

 restricted. Both methods receive at once, however, an 

 enormously extended range when the Protista are taken 

 into consideration. Then, moreover, we see the dawning 

 possibility of another method of investigation, that, 

 namely, of the chemical evolution of the organisms. Al- 

 ready some of the simpler Protista, the Bacteria, are 

 characterized and classified largely by their chemical 

 activities ; but in more complex organisms, in those which 

 have attained complete cell-structure, such as Protozoa, 

 the data of chemistry do not as yet supply the evolutionist 

 with a helpful method of investigation. 



The problem of cell-evolution may be attacked by the 

 help of the methods outlined in the foregoing remarks, 

 beginning with the consideration of the primary struc- 

 tural differentiation of the typical cell, the distinction of 

 nucleus, or rather chromatin, and cytoplasm. Since all 

 cells known to us exhibit this differentiation, we have three 

 possibilities as regards the manner in which it has come 

 about, which may be summarized briefly as follows : either 

 the cytoplasmic and chromatinic constituents of the cell 

 have arisen as differentiations of some primitive sub- 

 stance, which was neither the one nor the other ; or one 

 of these two substances is a derivative of the other, in the 

 course of evolution, either cytoplasm of chromatin, or 

 chromatin of cytoplasm. 



The idea of a primitive, undifferentiated protoplasmic 

 substance was first put forward by Haeckel, who em- 

 ployed for it the term "plasson" invented by Van Bene- 

 den™ to denote "la substance constitutive du corps des 

 Moneres et des cytodes . . . le substance formative par 



ioBuIL de VAcad. Boy. de Belgique, Second Series, Vol. XXXI (1871} d 



