Now these reptile-like fishes, of which gar-pikes are the living representatives, though of earlier appearance, are admittedly of higher rank than common fishes.  They dominated until reptiles appeared, when they mostly gave place to—­or, as the derivationists will insist, were resolved by divergent variation and natural selection into—­common fishes, destitute of reptilian characters, and saurian reptiles, the intermediate grades, which, according to a familiar piscine saying, are “neither fish, flesh, nor good red-herring,” being eliminated and extinguished by natural consequence of the struggle for existence which Darwin so aptly portrays.  And so, perhaps, of the other prophetic types.  Here type and antitype correspond.  If these are true prophecies, we need not wonder that some who read them in Agassiz’s book will read their fulfilment in Darwin’s.

Note also, in tins connection, that, along with a wonderful persistence of type, with change of species, genera, orders, etc., from formation to formation, no species and no higher group which has once unequivocally died out ever afterwards reappears.  Why is this, but that the link of generation has been sundered?  Why, on the hypothesis of independent originations, were not failing species re-created, either identically or with a difference, in regions eminently adapted to their well-being?  To take a striking case.  That no part of the world now offers more suitable conditions for wild horses and cattle than the Pampas and other plains of South America is shown by the facility with which they have there run wild and enormously multiplied, since introduced from the Old World not long ago.  There was no wild American stock.  Yet in the times of the Mastodon and Megatherium, at the dawn of the present period, wild horses and cattle—­the former certainly very much like the existing horse—­roamed over those plains in abundance.  On the principle of original and direct created adaptation of species to climate and other conditions, why were these types not reproduced, when, after the colder intervening era, those regions became again eminently adapted to such animals?  Why, but because, by their complete extinction in South America, the line of descent was here utterly broken?  Upon the ordinary hypothesis, there is no scientific explanation possible of this series of facts, and of many others like them.  Upon the new hypothesis, “the succession of the same types of structure within the same areas during the later geological periods ceases to be mysterious, and is simply explained by inheritance.”  Their cessation is failure of issue.

Along with these considerations the fact (alluded to on p. 114) should be remembered, that, as a general thing, related species of the present age are geographically associated.  The larger part of the plants, and still more of the animals, of each separate country are peculiar to it; and, as most species now flourish over the graves of their by-gone relatives of former ages, so they now dwell among or accessibly near their kindred species.