30 Geographical Distribution of Animals, 



step must be to examine minutely, whether the fishes of Lake Su- 

 perior are the same as those of other lakes, in this or any other 

 country ; and, if not, how they differ. To satisfy ourselves in this 

 respect, we shall successively examine all the families of fishes, 

 which have representatives in those great fresh- water seas. {Agassiz 

 on "Lake Superior, p. 246.) Professor Agassiz, after admirable 

 histories of the fishes of Lake Superior, concludes with the following 

 excellent observations : — * 



III. — General Observations; all Fresh-water Fishes of North Ame- 

 rica different from those of Europe — Lake Superior and the 

 Lakes north of it constitute a distinct Zoological District — 

 These Fishes have been created where they now live — Deductions 

 from this fact. 



Such a critical revision of the fishes of Lake Superior, and the 

 other great Canadian lakes, was the first necessary step in the in- 

 vestigation I am tracing, in order to ascertain the natural primitive 

 relations between them and the region which they inhabit. Before 

 drawing the conclusions which follow directly from these facts, I 

 should introduce a similar list of the fishes living in similar latitudes, 

 or under similar circumstances, in other parts of the world ; and more 

 particularly of the species of Northern Europe. But such a list, to 

 be of any use, should be throughout based upon a critical compara- 

 tive investigation of all the species of that continent, which would 

 lead to too great a digression. The comparison of the fresh-water 

 fishes of Europe, which correspond to those of North America, has 

 been carried so far, that I feel justified in assuming, what is really 

 the fact, that all the species of North America, without a single ex- 

 ception, differ from those of Europe, if we limit ourselves strictly to 

 fishes which are exclusively the inhabitants of fresh water. 



I am well aware that the salmon which runs up the rivers of 

 Northern and Central Europe, also occurs on the eastern shores of 

 the northern part of North America, and runs up the rivers empty- 

 ing into the Atlantic. But this fish is one of the marine arctic 

 fishes, which migrates with many others, annually further south, and 

 which migratory species is common to both continents. Those spe- 

 cies, however, which never leave the fresh waters, are, without ex- 

 ception, diff'erent on the two continents. Again, on each of the 

 continents, they differ in various latitudes ; some, however, taking 

 a wider range than others in their natural geographical distribution. 



The fresh-water fishes of North America, which form apart of its 

 temperate fauna, extend over very considerable ground ; for there is 

 no reason to subdivide into distinct faunae the extensive tracts of 

 lands between the arctics and the Middle States of the Union. We 

 notice over these, considerable uniformity in the character of the fresh- 



* "Lake Superior," p. 373. 



