The Food of the Smaller Fresh- Wafer Fishes. 83 



Nippeisink Lake and the Illinois River. Mud was found in notice- 

 able quantities only in a single specimen, and there in small 

 amount. About seventy per cent, of the food consisted of animal 

 sul>stances, three per cent, being fishes, taken by two of the 

 minnows. One had also eaten a small bivalve mollusk. Insects 

 made half the food, about one-third of them of terrestrial species 

 (Rhynchophora), the remainder being chiefly larv;e of ephemerids. 

 A few Chirouomus larvie and an aquatic hemipt(^r, were the only 

 other kinds determined. Crustacea amounted to thirteen per cent., 

 nearly all Ostracoda {(Jt/2)ris vidud^ taken by two of the speci- 

 mens from Chicago. Vegetable food stands at thirty-one per 

 cent., eaten by ten of the specimens. One-third of this consisted 

 of Alg;e, cliiefly of the filamentous forms, the remainder being 

 miscellaneous fragments of exogenous plants, chiefly evidently 

 aquatic. 



Local (Old individual peculiarities. — The general summari(,'s of 

 tiie food of so many individuals from so great a variety (jf situations 

 often disguise interesting and important facts relating to the food 

 resources of the species, since an element taken in large quantity 

 by one or two specimens may figure in the general average in 

 such an insignificant ratio as to lead to the inference tl;at its 

 occurrence is merely accidental. In other words, general averages 

 for a variety of situations will not necessarily indicate all the food 

 resources open to the species. These can only l)e demonstrated 

 by exhibiting the jiecnJiiiritic^ of the record as well as its 

 general avei'age characters. For example, the fact that only 

 eleven per cent, of the food of this species consisted of Alga' has 

 a somewhat different aspect wlien we learn that one of the speci- 

 mens had eaten nothing else, and that they made three-fourths of 

 the food of another. Three specimens liad eaten only insects, and 

 these made ninety per cent, or more of the food of three others. 

 Two iiad eaten nothing but Entomostraca, all the Ci/prlfi )iidua, 

 previously mentioned. Vegetable structures made the entire food 

 of four, and ninety per cent, or more of the food of three other 

 specimens. Three out of four individuals taken at Nippersink 

 Lake in May, had derived from ninety to one hundred per cent, of 

 their food from terrestrial lieetles of a single family (Rhynchoph- 

 ora), while ephemerid larvje occurred in the food of three others in 

 ratios exceeding seventy-five per cent. 



