I will not return to the surprising variety of species of fishes contained in this basin, though it is very difficult for me to familiarize myself with the idea that the Amazons nourishes nearly twice as many species as the Mediterranean, and a larger number than the Atlantic, taken from one pole to the other. I can no longer say, however, with precision, what is the exact number of species which we have procured from the Amazons, because, on retracing my steps as I descended the great river, I have seen fishes about to lay their eggs which I had seen at first under other conditions, and _vice versa_; and without consulting the collections made six months ago, and which are not now accessible to me, it is often impossible for me to determine from memory whether they are the same species, or different ones which escaped my observation in my first examination. However, I estimate the total number of species which I actually possess at eighteen hundred, and it may be two thousand.[94] But it is not only the number of species which will astonish naturalists; the fact that they are for the most part circumscribed within definite limits is still more surprising, and cannot but have a direct influence on the ideas now prevalent respecting the origin of living beings. That in a river like the Mississippi, which from the north to the south passes successively through cold, temperate, and warm zones,—whose waters flow sometimes over one geological formation, sometimes over another, and across plains covered at the north by an almost arctic vegetation, and at the south by a sub-tropical flora,—that in such a basin aquatic animals of different species should be met at various points of its course is easily understood by those who are accustomed to consider general conditions of existence, and of climate especially, as the first cause of the difference between animals and plants inhabiting separate localities. But that from Tabatinga to Pará, in a river where the waters differ neither in temperature nor in the nature of their bed, nor in the vegetation along their borders,—that under such circumstances there should be met, from distance to distance, assemblages of fishes completely distinct from each other, is indeed astonishing. I would even say that henceforth this distribution, which may be verified by any one who cares to take the trouble, must throw much doubt on the opinion which attributes the diversity of living beings to local influences. Another side of this subject, still more curious perhaps, is the intensity with which life is manifested in these waters. All the rivers of Europe united, from the Tagus to the Volga, do not nourish one hundred and fifty species of fresh-water fishes; and yet, in a little lake near Manaos, called Lago Hyanuary, the surface of which covers hardly four or five hundred square yards,