WHITEFISH OF THE LAKE OF GENEVA 



upon the leaves of large trees; the great family of 

 insects lives at the expense of the plants on which it 

 settles ; the links of the alimentary chain are but few. 

 In the former, on the other hand, there are no great 

 vegetables, or they are found only in small areas 

 near the shore; the initial synthesis, which is the 

 beginning of everything, cannot be based on them. 

 It is carried on by the microscopic, unicellular vege- 

 tables of the floating plankton. In spite of their 

 individual minuteness, the tremendous abundance of 

 them provides all that is needed. The alimentary 

 cycle begins with them and, since they are so small, 

 necessitates several degrees or stages. There we find 

 it as it actually is ; we realize how necessary it is, and 

 how it consists of a progressive series of successive 

 episodes. Life in the world of the waters, among the 

 beings which make up that world, shows us in greater 

 fullness, both its requirements and the power it has to 

 fulfil them. 



I have said, in my study of Daubenton, the founder 

 of Zootechnics, that the full activity of living Nature 

 consists in a continual series of exchanges of substances 

 and forces, of matter and energy. These exchanges 

 originate in the inorganic world, at the expense of 

 the elements which compose it and the radiations 

 which traverse it; they are carried on between in- 

 dividual and individual; they become more or less 

 vigorous as circumstances ordain, and finally end in 

 the destruction of death and the return to brute matter. 

 It is an endless cycle, always ceasing and always being 

 renewed, and in it the creatures of the living world 

 are themselves the bases of the exchanges, while the 

 effecting of them is itself their life. 



The best defined and most obvious of these ex- 

 changes is concerned with food. If creatures are to 

 grow, they must first produce the matter of which 

 they are composed, and then maintain its integrity 

 in spite of the fact that it is always being used up in 

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