The Food of Fishes. 
33 
from the Chicago market. Insects are also an important 
item — amounting to twenty-four per cent., nearly all be- 
ing the larvse of Neuroptera — Mayflies (Ephemeridse), 
dragon-flies and case-flies (Phryganekke). A single spec- 
imen from Peoria Lake had eaten one small fish---a 
“darter” of the genus Poecilichthys. 
The second group, twelve specimens from Lake Mich- 
igan, presents a curious and instructive contrast in food 
to the foregoing. Mollusks and insects wholly disappear, 
and Crustacea are limited to the commonest crawfish of 
the lakes (Cambarus virilis, Hagen), which forms four- 
teen per cent, of the food. The remaining eighty-six per 
cent, consisted wholly of fishes, all minnows (Cyprinidse) 
so far as recognized except one, and that was some unde- 
termined percoid — probably itself a perch. 
It will thus be seen that the common perch has a food 
history of three periods — the periods of infancy, youth, 
and mature age. In the first it lives wholly on Entomos- 
traca and the minutest larvse of Diptera; in the second,, 
commencing when the fish is about an inch and a half in 
length, it takes up first the smaller and then the larger 
kinds of aquatic insects in gradually increasing ratio, the 
cntomostracan food at the same time diminishing in im- 
portance; and in the third it appropriates, in addition, 
mollusks, crawfishes and fishes — in the lake specimens 
depending almost wholly on the last two elements. 
We have here the first instance of a fact which we shall 
see again and again illustrated — that the young, having 
at first an alimentary apparatus too small and delicate to 
dispose of any insects but the minutest larvse, live almost 
wholly on minute crustaceans. 
It is proper to note that the lake and river perch are by 
some good authorities regarded as separate species — the 
latter being much more highly colored than the former. I 
have not found so strict a separation of the two forms as 
that described by Mr. E. W. Nelson, but have frequently 
taken both in the same haul of the seine in different parts 
of Calumet R. and in Lake George, Ind. — a body of water 
communicating with Lake Michigan by an outlet three or 
four miles long. Occasional pale specimens are also tak- 
en far from the lakes, in the Fox and Illinois rivers. The 
