86 
The Food of the Smaller Fresh - Water Fishes. 
Summary of the Group. 
Taking now this group as a whole, we remark, first, the absence 
of mud mingled with their food, as related to the greatly dimin- 
ished length of the alimentary canal. We have now also a 
decided predominance of animal food, which is about three-fourths 
of the entire amount, and note likewise the first occurrence of 
fishes. Although Mollusca occur in this group, it is in quantity 
too small to appear in the ratios. Insects make about half the 
food of all, nine per cent, being terrestrial forms. The larvae of 
Neuroptera are by far the most important insect species, and 
stand at twenty-five per cent. Entomostraca make a fifth of the 
whole food, distributed among all the orders. The vegetation 
eaten was largely of a purely miscellaneous and incidental char- 
acter, only about a third of it being derived from aquatic plants. 
Group IV. 
Intestine short; teeth hooked, without grinding surface. 
This group, organized more strictly for predatory purposes than 
any of the preceding, contains also the largest number of genera, 
embracing nine of those occurring in Illinois. It was not thought 
necessary to study all of these, and my dissections were confined 
to five of them, namely: to Minnilus, Photogenis, Phenacobius, 
Semotilus and Ceratichthys. 
Minnilus atherinoides, Raf. Emerald Minnow. 
This species is everywhere abundant in streams and lakes, but 
does not occur in ponds. It is most common northward, swarm- 
ing in summer along the shores of Lake Michigan. 
The gill-rakers are short, triangular, and about one-fourth the 
length of the filaments; and the intestine is less than the length 
of the head and body. 
Eighteen specimens were studied, all from the northern half of 
the State. The food was almost strictly animal, but five per cent, 
consisting of vegetation, and this chiefly of accidental character, 
occurring in trivial ratios. Only a single specimen had taken 
about forty per cent, of its food from filamentous Algae. A 
minute fish had been eaten by one of these minnows. Insects 
