THE SUN-PERCH AND THE CATFISH 



to find it, it declines and its numbers grow less. And 

 all those which live side by side in any given place and 

 together find their subsistence, are bound together, so to 

 speak, by this sort of natural compact, which preserves 

 the equilibrium, giving to each the quota it needs. 

 They are really interdependent, as I said a moment ago ; 

 they do not confine themselves to living their own 

 individual lives ; they are component parts of an asso- 

 ciation formed by Nature, and within that association 

 are involved in a correlation which holds them all, 

 without exception, in its restraint. None can remain 

 aloof. 



" Now this equilibrium, and especially that of the 

 food supply, depends upon a balance which, in each 

 place, despite variations due to local circumstances, 

 remains practically constant. The arm of the river 

 before us, thanks to its vegetation, the tiny creatures 

 which hide in it, and the insects which fall into its 

 waters, is able to support a certain number of the fish 

 belonging to our species; but it can hold no more 

 because there would not be food enough for them. 

 The table is laid for a definite number of guests; they 

 eat up everything it has to offer, leaving not a scrap 

 behind. The conditions of Nature are such that all her 

 subjects, similarly affected by their need of nutrition, 

 absorb to the very last degree the resources she has to 

 offer. They automatically see to it that the table bears 

 exactly the right amount and no more. 



" Now you can see where we made our mistake. We 

 were so keen and so much in a hurry that we never 

 thought of this point. It was only later, by experience 

 and when we could not help realizing our failure, that 

 we started to investigate its cause, and so found out 

 what was wrong. It is not enough to put the fry in 

 the water; it is also essential to see that these little fish, 

 which later will grow into larger fish, find in the water 

 the necessary food. Only so much fry must be put into 

 the water as that water can support. It is not enough 

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