DISPERSION OF FRESH-WATER FISHES. Zj 



" The study of these features [of distribution] is of the 

 greatest importance, inasmuch as it may eventually lead 

 to a better understanding of the intentions implied in this 

 seemingly arbitrary disposition of animal life. . . . 



"There is still another very interesting problem re- 

 specting the geographical distribution of our fresh-water 

 animals, which may be solved by the further investigation 

 of the fishes of the Tennessee River. The water-course, 

 taking the Powells, Clinch, and Holston Rivers as its 

 head-waters, arises from the mountains of Virginia in 

 latitude 37° ; it then flows S. W. to latitude 34° 25', when 

 it turns W. and N. W., and finally empties into the Ohio, 

 under the same latitude as its source in 37°. 



" The question now is this : Are the fishes of this water 

 system the same throughout its extent? In which case 

 we should infer that water communication is the chief 

 condition of geographical distribution of our fresh-water 

 fishes. Or do they differ in different stations along its 

 course ? And if so, are the differences mainly controlled 

 by the elevation of the river above the level of the sea, or 

 determined by climatic differences corresponding to dif- 

 ferences of latitude? We should assume that the first 

 alternative was true if the fishes of the upper course of 

 the river differed from those of the middle and lower 

 courses in the same manner as in the Danube, from its 

 source to Pesth, where this stream flows nearly for its 

 whole length under the same parallel. We would, on 

 the contrary, suppose the second alternative to be well 

 founded if marked differences were observed between 

 the fish of such tracts of the river as do not materially 

 differ in their elevation above the sea, but flow under 

 different latitudes. Now, a few collections from different 

 stations along this river, like that sent me by Dr. New- 

 man from the vicinity of Huntsville, would settle at once 

 this question, not for the Tennessee River alone, but for 



