98 
Family PERCIDA. The Perches. 
This family consists, in this State, of three species,—the common 
yellow perch and the two species of pike-perch or ‘‘wall-eyed pike.’ 
I have examined the food of seventy-five specimens of this family, 
so distributed in time and space as to give a satisfactory idea of 
the usual food. 
Perca americana, Schrank. THe Common Perc. Rineup PercH 
This exceedingly well-known species is most abundant along the 
shores of Lake Michigan and in the small streams and lakes of the 
northeastern part of the State, becoming less common to the south 
and west. In the Illinois river at Peoria and Henry it occurs im 
limited numbers, but in Southern Illinois disappears so completely 
that even its name (there generally pronounced ‘‘pearch”) is trans- 
ferred to a different family, the sun-fishes (Centrarchid). 
My knowledge of the food of this species is derived from the study 
of the contents of forty-nine stomachs, of which thirty were from 
adults and the remaining nineteen from fishes ranging +% inch to 
four inches in length. ‘Ten. localities and as many dates are repre: 
sented by these specimens. Some were taken in the Illinois river, 
others in Lake Michigan and its southern tributaries, and still 
others in Fox river, at McHenry, and in the lakes connected with 
that stream. One lot included in these notes was bought in the 
Chicago market. They were evidently of the river form of the 
species, and, judging from the contents of their stomachs, which 
included a crustacean* not known to occur in Illinois, but found 
abundantly in Michigan, I conclude that they were from that State 
‘or from Wisconsin. } 
Food of the Young. 
Finding that the food of most fishes differs with age, I have 
grouped the young according to size, and averaged the food for each 
group separately,—the first group consisting usually of those undeg 
an inch in length, the second of those from one to two, ete. F 
Two perch under an inch in length had eaten nothing but Ente 
mostraca,—about equal quantities of Cyclops and Daphnias. I 
was not until the specimens reached an inch and a half in lengtk 
that insects of any considerable size appeared in the food. A single 
smaller fish had eaten a few minute larve of Chironomus, bu 
otherwise the food at thxs age consisted wholly of Entomostraca. 7 
About thirty-four per cent.' of the food of nine specimens ranging 
from 11 to 2 inches in length consisted of insects, and sixty-six pél 
cent. of crustaceans. The only insects recognized were the larva 
and pup of Chironomus (eleven per cent.), small water bugs—Corixa 
tumida, Uhl., C. alternata, Say, etc. (twenty-three per cent.), and @ 
trace of larve of May-flies (EKphemeride). The Crustacea wefe 
chiefly Cladocera and Copepoda—thirty-six per cent. and twenty. 
*Mancasellus tenax, Harger. | 
