74 
The Food of the Smaller Fresh - Water Fishes. 
seven of the specimens from Southern Illinois lakes. A consider- 
able quantity of unicellular Algm was also taken by one. Mol- 
lusks, eaten by two, were reckoned at five per cent., all Physa. 
Insects drop to fourteen per cent., chiefly undetermined larvae. 
No terrestrial forms were recognized. Corresponding to the 
greater development of the gill-rakers, we find the Entomostraca 
assuming greater importance in the food. These were reckoned 
at ten per cent.; three 'per cent, additional consisting of Cran- 
gonyx gracilis. 
FAMILY CYPRIN1DJE 
This family includes all the fishes properly known as “minnows,” 
embracing, in fact, by far the larger part of the smaller fishes of 
the State. Both in number and in variety of species it is much 
the most important family of fresh-water fishes. It includes, in 
Illinois, about forty species, nearly or quite one-fourth of the 
whole number known to occur in our territory. They occur in all 
waters from the Mississippi River and Lake Michigan to the 
smallest streams and ponds; but are much the most abundant in 
creeks and rivulets. The species differ greatly with respect to 
their favorite haunts, some affecting the principal lakes and larger 
rivers, others occurring most commonly in clear and rapid brooks, 
while still others are most frequent in the sluggish and muddy 
streams of prairie regions. The principal economic interest of the 
fishes of this family is due to the well-known fact that they fur- 
nish an important part of the food supply of larger species. 
But little has hitherto been done upon their food in the United 
States. In fact, I have seen nothing more accurate or comprehen- 
sive than the following general statement made by Prof. Cope, in 
his paper on the Cyprinidae of Pennsylvania :* 
“ These differences of habit are associated with peculiarities of 
food and of the structure of the digestive system. Few families 
of vertebrates embrace as great a variety in these respects as the 
present one. There are carnivorous, insectivorous, and graminiv- 
orous genera, which are distinguished as among mammalia, the 
former by the abbreviation, the last by the elongation of the ali- 
:;: 'Trans. Ainer, Philosophical Society, Vol. 13, New Series, page 353, 
