The Food of the Smaller Fresh - Water Fishes. 
85 
by those from Effingham. The fact has already been noted that 
one of the specimens had eaten only fishes. Five had confined 
themselves to an insect diet, while twelve had derived more than 
half their food from the vegetable kingdom, one of them eating 
ninety-five per cent, and another one hundred. 
Hemitremia heterodon, Cope. Northern Hemitremia. 
This species, extremely abundant in Northern Illinois, has not 
been taken by us south of .the central part of the State. North of 
Rock River it has been generally found in streams and lakes of all 
descriptions, from Lake Michigan down. 
The gill-rakers are few in number, but thick, triangular, and 
rather long, those on the posterior part of the arch being from a 
fourth to a third the length of the filaments. The intestine is 
contained one and one-fourth times in the length of the head and 
body. 
Eighteen specimens were studied, suitably distributed as to time 
and place. A little mud was found in the stomach of one. Only 
about one-tenth of the food consisted of vegetation, chiefly flowers 
and seeds. Traces of filamentous Algae occurred in two of the 
specimens. Univalve Mollusca were noticed in one, and insects 
in twelve, amounting to more than a fourth of the entire food. 
These were chiefly larvae of Chironomus (twenty per cent.), 
ephemerid larvae occurring in but one. Crustacea were reckoned 
at fifty-eight per cent., all Entomostraca, with the exception of a 
single Allorchestes denlata. About two-thirds of these were 
Cladocera, the remainder being Ostracoda and Copepoda. Roti- 
fers and Protozoa also rarely occurred, the latter including Centro- 
pyxis and Difflugia. Five of the specimens had eaten Entomos- 
traca only, and two others ninety per cent, or more. Only two 
had derived more than half their food from vegetable sources. 
It will be seen that the peculiar fact with respect to this species 
was the large per cent, of Entomostraca appropriated. I find 
nothing in the structure of the fish to explain this circumstance, 
other than the somewhat unusual development of the gill-rakers 
and the small size of the species. The latter probably had more 
to do with it than anything else. It should be noted, however, 
that nearly half the specimens were derived from places where 
Entomostraca were excessively abundant at the time of their 
capture. 
