Dispersion of Fresh-water Fishes 287 



southern latitudes a sufficient extent of uncongealed fresh 

 waters would flow by a short course into the ocean, to perserve 

 from destruction many forms of fresh-water fishes. Thus, 

 through many vicissitudes, the fauna of a given system of rivers 

 has had opportunity of uninterrupted descent, from the time 

 of the elevation of the mountain range, in which it has its 

 sources. . . . 



"As regards the distinction of species in the disconnected 

 basins of different rivers, which have been separated from an 

 early geologic period, if species occur which are common to 

 any two or more of them, the supporter of the theory of distinct 

 creations must suppose that such species have been twice 

 created, once for each hydrographic basin, or that waters flow- 

 ing into the one basin have been transferred to another. The 

 developmentalist, on the other hand, will accept the last propo- 

 sition, or else suppose that time has seen an identical process 

 and similar result of modification in these distinct regions. 



FIG. 186. Chub of the Great Basin, Leuasciis lineatus (Girard). Heart Lake, 

 Yellowstone Park. Family Cyprinidce. 



"Facts of distribution in the eastern district of North 

 America are these. Several species of fresh- water fishes occur 

 at the same time in many Atlantic basins from the Merrimac or 

 from the Hudson to the James, and throughout the Mississippi 

 Valley, and in the tributaries of the Great Lakes. On the other 

 hand, the species of each river may be regarded as pertaining 

 to four classes, whose distribution has direct reference to the 

 character of the water and the food it offers: first, those of the 

 tide-waters, of the river channels, bayous, and sluggish waters 

 near them, or in the flat lands near the coast; second, those of 

 the river channels of its upper course, where the currents are 



