DISPERSION OF FRESH-WATER FISHES. {1% 
common with that of the tributaries of Lake Michi- 
gan than it has with that of the Red River or the 
Arkansas. The influence of climate is again shown 
in the paucity of the fauna of the cold waters of 
Lake Superior, as compared with that of Lake 
Michigan. The majority of our species cannot 
endure the cold. In general, therefore, cold or 
Northern waters contain fewer species than South- 
ern waters do, though the number of individuals 
of any one kind may be greater. This is shown 
in all waters, fresh or salt. The fisheries of the 
Northern seas are more extensive than those of 
the Tropics. There are more fishes there, but 
they are far less varied in kind. The writer 
once caught seventy-five species of fishes in a 
single haul of the seine at Key West, while 
on Cape Cod he obtained with the same net 
but forty-five species in the course of a week’s 
work. Thus it comes that the angler, contented 
with many fishes of few kinds, goes to Northern 
streams to fish, while the naturalist goes to the 
South. 
But in most streams the difference in latitude is 
insignificant, and the chief differences in tempera- 
ture come from differences in elevation, or from 
the distance of the waters from the colder source. 
Often the lowland waters are so different in charac- 
ter as to produce a marked change in the quality 
of their fauna. These lowland waters may form a 
barrier to the free movements of upland fishes; but 
that this barrier is not impassable is shown by 
the identity of the fishes in the streams! of the 
1 For example, Elk River, Duck River, etc. 
