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THE AMERICAN NATURALIST [Vol. XLIX 



whereas the closely related Gastrotricha, Chatonoius, 

 eats minute particles of decayed animal and vegetable 

 matter, rarely taking diatoms. 



The smaller crustaceans in general and the snails are 

 scavengers, removing decaying algae and hits of dead in- 

 sects or other animal matter. The Cladocera, however, 

 are said to eat diatoms and many of the smaller algae. 

 Ostracoda are omnivorous and often attack their own 

 species. 



Among the insect members of this society, the larvae of 

 the may-flies and midges are the great herbivores, al- 

 though, in addition to algae, diatoms and leaves of higher 

 plants, consuming a great variety of vegetable sub- 

 stances, both living and dead. The great abundance of 

 Chironomus larvae make this genus an important factor, 

 both as a consumer, and as food for other animals. 

 Chironomus larvae and pupae are, in turn, eaten by dragon- 

 fly nymphs, and other predaceous larvae. They are of 

 much importance as fish-food. 



Dragon-fly nymphs are predatory. Some species eat 

 back-swimmers and water-boatmen, small crustaceans 

 and snails, coleopterous and dipterous larvae and even 

 young dragon-fly nymphs. The larger nymphs are eaten 

 principally by fish, occasionally by water-birds. 



This brief account of some of the feeding-habits will 

 serve to show how much all the members of this society 

 are dependent upon the others, and, at the same time, 

 are in constant danger of extinction. Each form acts as 

 a check upon too rapid multiplication of some other form. 

 Since the most prolific animals in this population are 

 Cyclops and Chironomus, each must have peculiarities 

 that enable it to survive in this environment and to com- 

 pete with other animals. Cyclops adapts itself easily to 

 changes. Its prolific reproduction, seasonal constancy, 

 and plasticity, give it great advantage over other small 

 Crustacea. Chironomus, also constant, prolific and adapt- 

 able, finds abundant food and comparative shelter among 

 the algal filaments. 



