WHITEFISH OF THE LAKE OF GENEVA 



the course of -their lives. They find it about them. 

 The smallest and simplest of them draw its elements 

 directly from the inorganic world; the others take 

 it ready made from creatures like themselves, which 

 they consume as prey. The chain of devourers and 

 devoured is thus begun, the chain by which living 

 matter passes successively into all, and incorporates 

 itself in them. The smallest are the beginning and the 

 end; the bond begins in them, and with them it is 

 completed. Their swarming mass, on land or in the 

 water, takes the predominant place. • 



Fig. 37. — Water-flea (Dapknia pulex), planktonic crustacean of the 

 t order Cladocera. Length between 1 and 5 millimetres. 



The carnivorous animals devour the herbivorous, 

 and these eat the plants nourished by brute matter; 

 their death makes everything brute matter again. 

 Each, compelled to take its place in this chain, has 

 a purpose there; Nature takes it as one link, and that 

 is all. Living matter thus acquires a life of its own, 

 independent of personal existence, and having its 

 origin in a life of general alimentation, in which 

 creatures play the part of alimentary transformers 

 for one another. The plant gathers mineral elements 

 and forms its substance out of them ; the herbivorous 

 animal modifies this substance and reconstitutes it in 

 itself for the benefit of the carnivorous animal. In the 

 general economy these different forms of flesh are 

 destined to be the objects of nutritive exchanges. The 

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