The Food of Fishes. 
32 
food of these specimens is probably due partly to the fact 
that they were all caught at the same time and place, and 
partly to the wintry weather when they were taken. 
Four specimens, from three and a half to four inches 
long, representing two localities and dates, had eaten a 
greater variety of articles, the food, in fact, now closely 
approaching that of the adult. Forty-five per cent, of the 
food was insects — chiefly larvae of May-flies — and fifty- 
five per cent. Crustacea — chiefly Amphipoda and Cladoc- 
era. Other insect elements were larvae of Chironomus, 
six per cent., and four per cent, of Corixas. The Cladoc- 
era were all Daphnia, and the Amphipoda were Allor- 
chestes dentata. A single specimen from Long L., near 
Pekin, 111., had eaten an isopod crustacean (Asellus). 
Cyprididae, another family of minute crustaceans, formed 
eight per cent, of the whole food of these specimens. 
Food of the Adult. 
The thirty mature individuals may best be treated in 
two groups, the first from streams and the second from 
Lake Michigan. 
Four of the first group were bought in the Chicago 
market, in March, 1880; six were taken from the upper 
Fox, in May; four were from Calumet R. at South Chi- 
cago, taken in August, 1878, and four were caught in 
October of that year, from the Illinois at Peoria. 
We notice, first, the entire disappearance of Entomos- 
traca, which are thus seen to be food proper to the young. 
We next observe the appearance of Mollusca (nineteen 
per cent.), which are evidently no insignificant food re- 
source of the species. Unio, Cyclas, Succinea, Physa het- 
erostropha, Say, and Valvata tricarinata , Say, are the 
mollusks recognized. Notwithstanding the lack of Ento- 
mostraca, Crustacea are the most important resource of 
these river specimens, constituting forty-eight per cent, 
of their food. Crawfishes (Cambarus) and our common 
little fresh-water shrimp (Palcemonetes exilipes, St.) 
compose ten per cent, of the whole; the previously no- 
ticed Allorchestes amounts to fifteen per cent. ; and spe- 
cies of Asellus, and Mancasellus tenax to twenty-three 
per cent. The Mancacelli were all from the specimens 
