The Food of the Smaller Fresh- Water Fishes. 85 



by those from Effiiiirham. The fact has already been noted that 

 one of the specimens iiad 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. 



Hemitrejiia heterodon, Cope. Nortiiekn Hemitremia. 



This species, extremely abundant in Northern Illinois, has not 

 been taken by us south of the central part of the State. Nortl\ 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 lenu-th 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 Algte 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 larv;e of Chironomus ( twenty per cent. ), 

 ephemerid larva; occurring in but one. Crustacea were reckoned 

 at fifty-eight per cent., all Entomostraca, with the exception of a 

 single Allorcli.ei^tes dentata. 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. 



