To Mr. George Ticknor.
Nahant, October 24, 1863.
my dear Sir,—Among the schemes which I have devised for the improvement of the Museum, there is one for the realization of which I appeal to your aid and sympathy.
Thus far the natural productions of the rivers and lakes of the world have not been compared with one another, except what I have done in comparing the fishes of the Danube with those of the Rhine and of the Rhone, and those of the great Canadian lakes with those of the Swiss lakes.
I now propose to resume this subject on the most extensive scale, since I see that it has the most direct bearing upon the transmutation theory. . . . First let me submit to you my plan.
Rivers and lakes are isolated by the land and sea from one another.
The question is, then, how they came to be peopled with inhabitants differing both from those on land and those in the sea, and how does it come that every hydrographic basin has its own inhabitants more or less different from those of any other basin?
Take the Ganges, the Nile, and the Amazons.
There is not a living being 