The Food of the Smaller Fresh- Water Fishes. 
83 
Nippersink 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 
substances, 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 larvae of ephemerids. 
A few Chironomus larvae and an aquatic hemipter, were the only 
other kinds determined. Crustacea amounted to thirteen per cent., 
nearly all Ostracoda ( Cypris vidua) 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 Algae, chiefly of the filamentous forms, the remainder being 
miscellaneous fragments of exogenous plants, chiefly evidently 
aquatic. 
Local and individual pecidiarities. — The general summaries of 
the food of so many individuals from so great a variety of 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 that 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 be demonstrated 
by exhibiting the peculiarities of the record as well as its 
general average characters. For example, the fact that only 
eleven per cent, of the food of this species consisted of Algm has 
a somewhat different aspect when 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 had eaten only insects, and 
these made ninety per cent, or more of the food of three others. 
Two had eaten nothing but Entomostraca, all the Cypris vidua 
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 beetles of a single family (Rhynchoph- 
ora), while ephemerid larvrn occurred in the food of three others in 
ratios exceeding seventy-five per cent. 
