ii6 THE ORIGIN AND EVOLUTION OF LIFE 



for a Ciliate, like every other protozoan, is a complete and 

 independent organism, and is specialized for each and all of 

 the vital functions performed by the higher multicellular or- 

 ganisms as a whole. 



In the chemical life of the Protozoa^ (Amceba) the proto- 

 plasm is made up of colloidal and of crystalloidal substances 

 of different density, between which there is a constant, orderly 

 chemical activity. The relative speed of these orderly proc- 

 esses is attributed to specific catalyzers which control each 

 successive step in the long chain of chemical actions. Thus 

 in the breaking-down process (destructive metabolism) the by- 

 i:)roducts act as poisons to other organisms or they may play 

 an important part in the vital activities of the organism itself, 

 as in the phosphorescence of Noctiluca, or as in reproduction 

 and regeneration. Since regrowth or regeneration- takes place 

 in artificially separated fragments of cells in which the nuclear 

 substance (chromatin) is believed to be absent, the formation 

 of new parts may be due to a specific enzyme, or perhaps to 

 some chemical body analogous to hormones and formed as a 

 result of mutual interaction of the nucleus and the protoplasm. 

 Reproduction through cell-division is also interpreted theoreti- 

 cally as due to action set up by enzymes or other chemical 

 bodies produced as a result of interaction between the nucleus 

 and cell body. The protoplasm is regenerated, including both 

 the nuclei and the cell-plasm, by the distribution of large quan- 

 tities of nucleoproteins, the specific chemical substance of 

 chromatin. 



The latest word as to the part played by natural selection 

 in the heredity-chromatin is that of Jennings^ who, after many 

 years of experiment, has proved that the congenital charac- 



I Calkins, Gary N., 1916, p. 260. = Op. cit., pp. 261-264, 266. 



3 Jennings, H. S., 1916, pp. 522-526. 



