DISPERSION OF FRESH-WATER FISHES. IO/ 



explained, in a word, by the hypothesis of the progressive 

 adaptation of the young of certain Percidcz to a peculiar 

 place of refuge and a peculiar food-supply. 



" Perhaps we may, without violence, call these the 

 mountaineers among fishes. Forced from the populous 

 and fertile valleys of the river beds and lake bottoms, they 

 have taken refuge from their enemies in the rocky high- 

 lands, where the free waters play in ceaseless torrents, and 

 there they have wrested from stubborn Nature a meagre 

 living. Although diminished in size by their continual 

 struggle with the elements, they have developed an ac- 

 tivity and hardihood, a vigor of life, and glow of high 

 color almost unknown among the easier livers of the lower 

 lands." 



It is noteworthy that among the European gen- 

 era of Percidce, one of them, Aspro, has assumed 

 a similar habitat, and adapted apparently as a 

 result of its surroundings characters similar to 

 those of Etheostoma. It is not likely that Aspro is 

 an ancestor of Etheostoma, still less likely that A s- 

 pro is descended from the latter genus. The simi- 

 lar development of the two seems rather a case of 

 analogous variation, the influence of similar condi- 

 tions in different places on similar organisms. 



It is remarkable, also, that in mountain regions 

 in which no Percidce are found, fishes very similar 

 to the Darters in appearance and habits, though 

 totally different in structure, have by analogous 

 agencies been developed. Loaches, Cat-fishes, 

 Gobies, Characins, Sculpins, in different parts of 

 the world inhabit swift mountain streams, and in 

 a similar way become dwarfed and concentrated, 

 taking the place in their respective habitats which 



