The Necton 313 



planctonts ; but we still are sadly lacking in knowledge 

 of the conditions that make for their abundance. 



II 



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 muskellonges 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 thru. 

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

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



