26 The Food of Fishes. 



ronomus larvae, twenty-seven per cent, larvae of small 

 ephemerids, and twelve per cent, of Oopepoda (Cyclops;. 



Boleichthys elegmis^ found only in the southern part of 

 the state (three specimens examined), had eaten only dip- 

 terous larvas (thirty-seven per cent.) and ephemerid larvae 

 (sixty-three percent.). This is a larger, heavier species 

 than most of the others, and, therefore, like Alvordius, 

 prefers ephemerids to gnats. 



Last and least comes Microperca punctulata^ represented 

 by nine specimens from four localities in northern Illinois. 

 This smallest of the darters shares with Percina, the largest, 

 the peculiarity of a large ratio of crustacean food, which 

 made up sixty-four per cent, of the total. The principal 

 kinds were Cyclops, Chydorus, young Oammarus fasciatus^ 

 Say, and young Crangonyx gi'acilis^ Smith. The remain- 

 ing elements were Chironomus larvae (thirty-four per cent.) 

 and a trace of ephemerids (two per cent.). 



It will be seen that the family, taken as a whole, divides 

 into two sections, distinguished by the abundance or defi- 

 ciency of crustacean food. This is easily explained by the 

 fact that Percina and Microperca range much more freely 

 than the other genera, being frequently found among 

 weeds and algae in comi3aratively slow water with muddy 

 bottom, while the others are rather closely confined to swift 

 and rocky shallows. 



In discussing the food of the whole group, taken as a 

 unit, it may best be compared with the food of the young 

 of other percoids. It is thus seen to be remarkable for 

 the predominance of the larvae of Chironomus and small 

 Ephemeridae — the former of these comprising forty-four 

 per cent, and the latter twenty-three per cent, of the 

 whole food of the seventy specimens. In young black bass 

 {Micropterus pallidus)., on the other hand, the averages of 

 nine specimens, ranging from five eighths inch to one and 

 a half inches in length, were, in general terms, as follows : 

 Cladocera forty-two percent., Copepoda seven percent., 

 young fishes twenty per cent., Corixa and young Notonecta 

 twenty-nine per cent., and larval Chironomus only two per 

 cent. The search for the cause of this difference leads nat- 

 urally to an examination of the whole economy of these 



