DISPERSION OF FRESH-WATER FISHES. 1 05 



The large group or genus of Darters l 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 2 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-larvae 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 



* Etheostoma. 



2 A Catalogue of the Native Fishes of Illinois. Report of thr 

 Illinois Fish Commissioners, 1884, p. 95. 



