DISPERSION OF FRESH-WATER FISHES. 87 
“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 
