700 The Food of the Darters. [October, 
Gammarus fasciatus Say, and young Crangonyx gracilis Smith. 
The remaining elements were Chironomus larve (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 presence or absence of crusta- 
cean 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 Algz in comparatively 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 per- 
coids. It is thus seen to be remarkable for the predominance of 
the larve of Chironomus and small Ephemerida—tie 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: Clado- 
cera forty-two per cent., Copepoda seven per cent., 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 naturally to an examination of 
the whole economy of these little fishes, and opens up the ques- 
tion of their origin as a group.. 
The close relation of the Etheostomatine to the Percide 
proper, requires us to believe that the two groups have but 
recently diverged, if, indeed, they are yet distinctly separate. 
We must inquire, therefore, into the causes which have oper- 
ated upon a group of percoids to limit their range to such appa- 
rently unfavorable situations, to diminish their size, to develop 
unduly the paired fins and reduce the air-biadder, to remove the 
scales of several species more or less completely from the head, 
breast, neck and ventral region, and to restrict their food chiefly 
to the few forms mentioned above. : 
No species can long maintain itself anywhere which cannot, 1n 
some way, find a sufficient supply of food, and also protect itself 
against its enemies. In the contest with its enemies it may 
acquire defensive structures or powers of escape sufficient for its 
protection, or a reproductive capacity which will compensate for 
