CYPRINHLE THE MINNOWS AND THE CARP 95 



The minnow family, much the largest and most complex of 

 the fish families of the state, has become variously differentiated 

 in respect to habits, ecological relations, and some of its more im- 

 portant structures, in a way to adjust the group with consider- 

 able exactness to the various features of its environment. In 

 respect to territorial distribution, we may distinguish among the 

 minnows a group distributed mainly through the Mississippi 

 drainage, another mainly through the Ohio drainage, and a third 

 which is generally distributed throughout the state. We may 

 also distinguish a group of species which does not enter or remain 

 in the persistently turbid waters of the southern Illinois region 

 covered by the fine-grained drift of the lower Illinoisan glacia- 

 tion; another group which is common in the lowland lakes, and 

 a much larger group which is rarely found in lakes of any kind; 

 a group of minnows which prefer large rivers, and another which 

 is most abundant in the smaller streams; one more than nor- 

 mally common over a mud bottom, and another evidently 

 most at home over a bottom of rock and sand ; one which prefers 

 a swift current, and another which seeks quiet waters. 



The various species of the family show also considerable 

 differences of preference in respect to the kinds of food which 

 they choose from the general supply offered to them. They are 

 mainly carnivorous, on the whole, in this country, although we 

 have found fishes and mollusks only rarely in the food of our 

 native species. Insects and crustaceans, including Entomos- 

 traca, are their principal dependence, except for a few which 

 eat largely of vegetation and a few others which feed almost 

 wholly on the highly organic mud of the bottoms of our ponds 

 and streams. The special structures of alimentation corre- 

 spond in their variations, in the several divisions of the family, 

 to these differences of their food. 



Fishes so small as most of our minnows, are, as a rule, in no 

 need of a specially developed set of gill-rakers, since the gill- 

 arches themselves are so small and the spaces between them so 

 narrow that any object large enough to be useful for food is little 

 likely to be carried out through the gills with the respiratory 

 current. In two of our species, however (Abramis crysoleucas 

 and Notropis heterodori), the gill-rakers are considerably de- 

 veloped, and in these species Entomostraca appear more largely 

 in the food than in any other minnows. Even Protozoa and 

 unicellular algae have been found common in the stomachs of 

 N. heterodon. 



