24 
The Food of Fishes. 
I shall give here a description of the food of the family, 
based upon a study of the contents of seventy stomachs 
representing fifteen species, collected in all parts of Illi- 
nois, in several months of four successive years. These 
indicate much more than their number would imply, since 
from those collected at each time and place, as many were 
commonly studied as were necessary to give a full idea of 
the food of the species then and there. The different in< 
dividuals from the same date and locality usually agreed 
so closely in food, that the study of from two to five gave 
all the facts obtainable from several times as many. The 
data here given, therefore, really exhibit the food of the 
family at different seasons in twenty-nine localities with- 
in the State. 
The genus Pleurolepis is comparatively rare in Illinois 
as there are few of the sandy streams in the State, which 
it inhabits. Seven individuals were examined — four of 
P. pellucidus and three of P. asprellus. The food of these 
specimens was remarkably uniform — the only elements 
found being the larvae of small Diptera and ephemerids. 
Eighty-one per cent, of the food of all consisted of the 
larvae of Chironomus* — a small, gnat-like insect — twelve 
per cent, of the larvae of other small Diptera, and the re- 
maining seven per cent, of ephemerid larvae (May -flies). 
Twelve specimens of the genus Alvordius were studied 
— seven of maculatus and five of phoxocephalus. These 
represented five different localities and dates. This is a 
larger species than the preceding, and to this fact is prob- 
ably due the predominance (seventy-five per cent.) in its 
food of the larvae and pupae of May-flies (Ephemeridae). 
These included four per cent, of the larvae of Palingenia 
hilineata, Say, one of the largest ephemerids in our 
streams. The remaining kinds were larvae of dragon- 
flies (Agrionidae), four per cent., larvae of Chironomus, 
seven per cent., Corixa tumida, Uhl., thirteen per cent., 
and Cyclops, one per cent. 
• The larvae of Chironomus are among the most important elements of 
fish food in our waters, appearing in abundance in the stomachs of the 
young of a great variety of species. They have been too little studied 
in this country to allow specific determination. 
