538 On some Entomostraca of Lake Michigan [July, 



prived of this resource for the nourishment of their young, fishes 

 would be reduced to an insignificant remnant of their present 



Immense quantities of them are also taken by adult fishes, 

 especially in earl)' spring, and some of the largest species make 

 them a principal dependence. The shovel fish (Polyodon) of our 

 great central rivers — a giant among inland fishes — engulfs untold 

 myriads of them at a meal — thus performing in fresh water the 

 functions of the whale in the great seas. In the lakes of Europe 

 they are the main food resource of several deep water salmonoids, 

 while in our own great lakes, clouds of the higher crustaceans 

 (Mysis) live wholly at their expense; and these Mysidae, again, 

 contribute largely to the maintenance of the whitefish and black- 

 fin, and other important species. Some insect larva; likewise 

 prey upon them ; and amphipod crustaceans, while they seem to 

 feed chiefly, upon vegetable structures of one sort or another, 

 certainly sometimes attack and devour entomostraca with a sur- 

 prising ferocity. Mollusca, one would say, could afford to be 

 indifferent to them, since they neither eat them nor are eaten by 

 them, nor seem to come in contact with them anywhere, through 

 any of their habits or necessities. But for this very reason these 

 two classes afford an excellent illustration of the stringent system 

 of reactions by which an assemblage of even the most diverse 

 and seemingly independent organisms is held together. To say 

 nothing of the fact that both groups feed to a considerable extent 

 upon the same kinds of food, and thus probably limit each other's 

 multiplication, in some degree, the further fact that vast quanti- 

 ties of both are destroyed by fishes, brings them into a mutually 

 hostile relation. If there were no entomostraca 'for young fishes 

 to eat, there would be very few fishes indeed to feed upon mol- 

 lusca, and that class would flourish almost without restraint; while,, 

 on the other hand, if there were no mollusca for the support o\ 

 adult fishes, entomostraca would be'relieved from a considerable 

 part of the drain upon their numbers, and would multiply ac- 

 cordingly. 



It is through their intervention that fishes and certain car- 

 nivorous plants are brought into apparent competition. T e 

 insect larva- destroyed by 



the bladder-wort in some situations where the plant fills acres < 

 the water, must be prodigious, taking the season through ; and 1 



