32 The Food of Fishes. 



tliat 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 Oladoc- 

 era. Other insect elements were larvae of Chironomus, 

 six per cent., and four per cent, of Oorixas. The Cladocera 

 were all Daphnia, and the Amphipoda were Allorchestes 

 dentata. A single specimen from Long L., near Pekin, 

 111., had eaten an isopod crustacean (Asellus). Oyprididas, 

 another family of minute crustaceans, formed eight per 

 cent, of the whole food of these specimens. 



Fo od 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 mar- 

 ket, in March, 1880 ; six were taken from the upper Fox, 

 in May; four were from Calumet R. at South Chicago, 

 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 mol- 

 lusks recognized. Notwithstanding the lack of Entomos- 

 traca, 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 {Palmmo^ietes exiUpes., St.) compose ten per 

 cent, of the whole ; the previously noticed Allorchestes 

 amounts to fifteen per cent. ; and species of Asellus, and 

 Mancasellus teriax to twenty-three per cent. The Manca- 

 celli were all from the specimens from the Chicago market. 



