92 
almost indifferently whatever edible things the water contains whic 
its habitual range and its peculiar alimentary apparatus enable it te 
appropriate, and eating of these in about the ratio of their relative 
abundance and the ease with which they can be appropriated at any 
time and place. If this is so, knowing the structure of a fish an 
the contents of a body of water, we shall be able to tell, a priorr, 
what the fish will eat if placed therein. 
This is, in fact, the objective point of the present investigation,— 
to arrive at a knowledge of the correlations of structure and food 
habits sufficiently detailed and exact to make the tedious and diffi- 
cult labor of examining the contents. of stomachs unnecessary here- 
after. Some generalizations of this sort are given in the following 
pages, and others relate to genera not included in this report. 
The method of this paper differs from that of the previous one 
referred to by the calculation of the ratios of the different kinds of 
food for each species or group of individuals. These ratios were 
obtained by averaging careful estimates of the relative amounts of 
the different food elements found in each stomach. 
It is proposed to follow a similar method hereafter down through 
the remaining orders of the class. Most of the material has been 
collected for this purpose, and much of it has been already studied. 
OrpeR THLEOCEPHALI. 
Suborder ACANTHOPTERI. 
This suborder includes all Dlinois fishes which have the anterior 
dorsal fin (where there are two) or the first rays of the dorsal 
(where there is but one) stiff, spinous and sharp, and united by an 
evident membrane; excepting only the remarkable “brook silver- 
sides,’ which is placed by Drs. Gill and Jordan in another croup. 
It embraces all our game fishes except those belonging to the pick- 
erel family (Hsocide) and the salmon family (Salmonide). Its prin- 
cipal members are the darters, the various species of perch and 
bass, the sunfishes and the sheepshead. Forty-six species of the 
grder have been collected in the State, but only thirty-four of these 
re common enough to form features. of any importance in our fish 
fauna. 
The most numerous family of the group is the Centrarchide (sun- 
fishes); the most important species are the two kinds of black bass, 
the pike-perch or ‘‘wall-eyed pike,”’* the common perch, the white 
bass, and the croppie or silver bass. 
The following account of the food of this suborder is based upon 
the careful microscopic study of the contents of four hundred 
and twenty-five stomachs, representing six families, twenty generat 
and thirty-three species. : 
*It is generally to be desired that the absurd names of “Salmon” and “Jack Salmon” 
for these species should be suppressed. They might as well be called suckers or catfishes 
or minnows, as tar as accuracy is concerned. Common names are many times harder to 
kill than the eat of the proverb, however; and itis probable that unnumbered generations 
has continue to call the pike-perch ‘‘salmon”; the sunfishes, “perch”; and the black bass, 
oe rout,’ 
t The classification of this paper is substantially that of Jordan’s Manual of the Verte- 
brates of North America, etc., Ed. 2, 1878. ; 
