THE SUN-PERCH AND THE CATFISH 



a good deal. Like the eel, it can dig itself into the mud 

 of a pond for weeks and months at a time, brave the 

 droughts of summer or the cold of winter. Like the eel, 

 it can adapt itself to waters of every kind, even the 

 foulest, provided it can satisfy its hunger there. The 

 slightest little trickle of water is sufficient for its fry 

 when they are young and small. In certain places 

 where there are carp-ponds, the presence of this species 

 has become a genuine plague, interfering with breeding 

 and compelling the breeders to take expensive measures 

 to counteract it. Yes, all in all, this catfish is not exactly 

 an acquisition to be proud of." 



Fig. 42. — The Char. The usual length is from 10 to 20 inches. 



The son was sitting on the grass, leaning against a 

 tree, listening attentively and enjoying the shade so 

 conducive to conversation. " There must be a reason 

 for these curious differences," he said. " How is it that 

 some of the acclimatized fish get on well while others 

 don't? In the country of origin they are on the same 

 footing; they all live quite well there. It is surprising 

 that when they are transplanted elsewhere they get on so 

 differently. What is the cause of it ? " 



" That's what I was getting at," replied the father. 

 " I will tell you as far as I can. I will begin with a com- 

 parison. Think, for a moment, of the body which all 

 creatures possess. It is made up of juxtaposed organs, 

 each with its function, fulfilling that function in order 

 to play its part in life as a whole. Again, each of them 

 has its own shape, its own structure, its own size; there 

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