“Another family very abundant in various parts of the world is that of the Perches. They are found all over North America, Europe, and Northern Asia; but there is not one to be found in the fresh waters of the southern hemisphere. In South America and in Africa they are represented however by a very similar group, that of the Chromids. These two groups are so much akin that from their structure it would seem natural to suppose that the Chromids were transformed Perches; the more so, since in the western hemisphere the latter extend from the high north to Texas, south of which they are represented by the Chromids. Here the geographical as well as the structural transition would seem an easy one. But look at the eastern hemisphere. Perches abound in Asia, Europe, and Australia, but there are no Chromids there. How is it that the Perches of this continent have been so fertile in producing Chromids, and the Perches of all other continents, except Africa, absolutely sterile in this respect? Or if we reverse the proposition, and suppose the Perches to have grown out of the Chromids, why have their ancestry disappeared so completely on the Asiatic side of the world, while they do not seem to have diminished on this? And if Perches and Chromids should be represented as descending from an older common type, I would answer that Palæontology knows nothing of such a pedigree. “Next come the Chubs, or in scientific nomenclature the Cyprinoids. These fishes, variously called Chubs, Suckers, or Carps, abound in all the fresh waters of the northern hemisphere. They are also numerous in the eastern part of the southern hemisphere, but have not a single representative in South America. As the Goniodonts are characteristic of the southern hemisphere in its western half, so this group seems to be characteristic of it in its eastern half. But while the Cyprinoids have no representative in South America, there is another group there, structurally akin to them, called the Cyprinodonts. They are all small-sized; our Minnows belong to this group. From Maine to Texas they are found in all the short rivers or creeks all along the coast. It is for this reason that I expect to find the short coast rivers of South America abounding in Minnows. I remember to have found in the neighborhood of Mobile no less than six new species in the course of an afternoon’s ramble. These fishes are almost all viviparous, or at least lay their eggs in a very advanced state of development of the young. The sexes differ so greatly in appearance that they have sometimes been described as distinct species, nay, even as distinct genera.[12] We must be on our guard against a similar mistake. Here again we have two groups, the Cyprinoids and Cyprinodonts, so similar in their structural features that the development of one out of the other naturally suggests itself. But in South America there are no Cyprinoids at all, while the