AND ITS INHABITANTS 87 



a complex interaction of physicochemical laws which do not 

 differ fundamentally from the so-called laws operating in the 

 inorganic world. 



Individuality of organisms. We have seen that, although 

 all protoplasm has a similar fundamental physicochemical 

 basis, nevertheless there is a considerable, indeed a great, di- 

 versity in the minor details of its composition, not only in 

 different species of animals and plants, but also in the various 

 parts of the same animal or plant. In fact, organisms are 

 organisms because of specific local differentiations in the imme- 

 diate substratum of their vital activities. 



This specification of protoplasm is rendered possible by the 

 fact that the structural units of all organisms are microscopic 

 masses of protoplasm, termed cells. The bodies of all higher 

 animals and plants are congeries of millions of these proto- 

 plasmic units, while many of the simpler forms of life consist 

 of but a single one. Therefore it is apparent that a funda- 

 mental characteristic of organisms as we know them today is 

 not only that the material basis of their activities which we 

 call life is the somewhat protean, though no less real, proto- 

 plasm, but also that this physical basis is individualized into 

 structural moieties, the cells. It is not an overestimation to 

 say that the recognition of this dual similarity of physico- 

 chemical and morphological organization of all living things 

 must be considered the greatest single generalization which 

 biological science has attained, and must be ranked with the 

 theory of organic evolution, of which it is the corner-stone, in 1 

 its far-reaching bearings. 4 



4 See Allen, F. J., op. cit. 



Minchin, E. A., The evolution of the cell. Amer. Nat., vol. 50, 1916, 

 pp. 5-38, 106-118, 271-283. 



Conklin, E. G., The basis of individuality in organisms from the stand- 

 point of cytology and embryology. Science, new ser., vol 43, 1916, 

 pp. 523-527. 



Driesch, H., The problem of individuality, 1914. 



