DISPERSION OF FRESH-WATER FISHES. 105 
The large group or genus of Darters! is com- 
posed of small, brilliantly colored Perches, whose 
structure is especially adapted for life on the 
rocky bottoms of small clear streams. The re- 
lations of these species to the typical Perches 
have been admirably discussed by Professor S. A. 
Forbes, from whose paper? I make the following 
quotations : — 
“We must inquire, therefore, into the causes which have 
operated on a group of Percoids to limit their range to 
such apparently unfavorable conditions, to diminish their 
size, to develop unduly the paired fins and reduce the 
air-bladder, to remove the scales of several species more 
or less completely, . . . and to restrict their food chiefly 
to a few forms [of insect-larve and crustacea]. 
“No species can long maintain itself anywhere which 
cannot in some way find a sufficient supply of food and 
also protect itself against its enemies. In its contests 
with its enemies it may acquire defensive structures or 
powers of escape sufficient for its protection, or it may 
become adapted to some place of refuge where other 
fishes will not follow. What better refuge could a har- 
assed fish desire than the hiding-places among stones in 
the shallows of a stream where the water dashes cease- 
lessly by with a swiftness few fish can stem? And if at 
the same time the refugee develop a swimming power 
which enables it to dart like a flash against the strongest 
current, its safety would seem to be insured. But what 
food could it find in such a place? Let us turn over the 
stones in such a stream, sweeping the roiled water at the 
same time with a small cloth net, and we shall find larva 
1 Etheostoma. 
2 A Catalogue of the Native Fishes of Illinois. Report of the 
Illinois Fish Commissioners, 1884, p. 95. 
