The Ned ok 313 



THE NECTON 



The large free swimming animals of the fresh waters 

 are all fishes. Indeed, as we have already noted (p. 

 233), but a few of the fishes range through the open 

 waters. Such are the white-fish, the ale-wife and the 

 ciscos, — all plancton feeders, — and a few more 

 piratical species, like the lake trout and the muskel- 

 longes that feed mainly on smaller fishes. 



Necton, it will thus be seen, is not a natural society. 

 It contains no producing class. It is sustained by the 

 plancton and by the products of the shores. 



These fishes all have a splendid development of 

 stream-line form. They all swim superbly. And 

 according as they feed on plancton or on other fishes 

 they are equipped with plancton strainers or with 

 raptorial teeth. Excellent plancton strainers are those 

 of the lake fishes. They are composed of the close-set 

 gill-rakers on the front of the gill arches, and they 

 strain the water passing through. This mesh is adapt- 

 ed for straining the larger animal planctonts while let- 

 ting the lesser chlorophyl-bearing forms slip thro. 

 Thus the fishes reap the crop of animals that is matur- 

 ed, without destroying the sources for a crop to come. 



