the magnolia in Mexico; 40°-50° of latitude separate the extremes which meet in the Himalayas, and the vast plains and huge river systems seem almost to solicit immigration. The accordance of the whole faunas of Mexico and Guiana, moreover, shows how little the isthmus of Panama checks the advance to South America, where again one mighty fluvial system trenches upon the other without any lofty partitions; nor is there any arid desert in the whole extent from the Canadian seas to Patagonia.

"We shall probably not be wrong in ascribing the remarkable extension of fossil and present mammals of America in a great measure to this circumstance. As we have seen, the Miocene fauna of Nebraska is the offspring of the Eocene fauna of the Old World. The Pliocene animals of Niobrara, which are buried in the same district as Nebraska, but on more recent arenaceous strata, still further corroborate this statement: elephants, tapirs, and many species of horses, scarcely differ from those of the Old World; the pigs, judging by their dentition, are descendants of European miocene Palæochoridæ. The ruminants are represented by the same genera, and partially by the same species, as in the analogous strata of Europe, as deer, sheep and buffaloes; neither do the carnivora or the minute animal life offer an exception. Many genera of an entirely Old-World cast have in the lapse of time penetrated far into South America, and there died out shortly before the arrival of man, or perhaps by his co-operation, as was the case with the two species of mammoth of the Cordilleras and the South American horse, whose present successors reached this insular continent by a

far shorter road. Even a species of antelope and two other horned ruminants (Leptotherium) found their way to Brazil. Two sorts of tapir, of which the dentition, even in Cuvier's eyes, is scarcely distinguishable from the Indian species; two species of pigs, still bearing in their milk-teeth unmistakable characters of their aboriginal form; and a number of deer, besides the lamas, a later and originally American offshoot of the Eocene Anoplotheria-are one and all living remnants of this ancient colony from the East, which did not reach its dwelling-place without copious losses on its long pilgrimage. It can scarcely be doubted that many of the beasts of prey which in the Diluvium of South America retained their family character more than they do now, must have arrived there in the same manner. Let us now remember that even the Eocene Canopithecus of Egerkingen distinctly pointed to the present apes of America, and that the Didelphida (Opossums) lie buried in the same European soils. It might almost appear that it was pre-eminently the division of arboreal quadrumana which, with the opossums, domesticated itself in the vast forests of their new abode, and, receiving a fresh impulse, gave rise to a multitude of special forms, without however having, even in the present times, reached the pitch of development attained by their cousins who had remained behind in the Old World.

"We may now appropriately return to our previous remark that this migration of animals did not find the south of the New World destitute of mammals, but rather already occupied by the toothless representatives of antarctic, or at least of southern animal life. The

diluvial fauna of South America collected by Lund, Castlenau, and Weddell, from the Brazilian caves, and the alluvium of the Pampas, among the 118 species cited, actually includes, in addition to those already mentioned, as being of probably Old-World pedigree, no less than 35 species of Edentata, and these animals of considerable bulk. Not reckoning the 36 rodents and bats, and the smaller fauna in general, they constitute nearly half of the larger diluvial animals of South America. The assemblage of Edentata previously settled in these regions thus held their own against the invasion from the north.

It is comprehensible that the same external causes which led the march of the children of the north constantly further, may likewise have invited the members of the antarctic fauna to extend themselves northwards. As we even now encounter the incongruous forms of the sloth, the armadillo, and the ant-eater in Guatemala and Mexico, in the midst of a fauna in great part consisting of races still represented in Europe, we also find, even in diluvial eras, gigantic sloths and armadillos ranging far into the north. Megalonyx Jeffersoni, and Mylodon Harlemi, sentries of South American origin thrown out as far as Kentucky and Missouri, are a phenomenon as heterogeneous in the land of the bison and the deer, as is the mastodon in the Andes of New Granada and Bolivia. Over the whole enormous extent of both portions of the New Continent, the mixture and interpenetration of two mammalian groups of completely diverse families, constitutes the most conspicuous feature of its fauna; and it is significant that each group increases in the abundance of its representatives

and in the originality of their appearance as we approach its point of derivation."

Hence, on both sides of the ocean, north of the very sinuous boundary of the antarctic or southern fauna, we find ourselves still in the midst of the diluvial animal world, which extended itself, by a bridge in the vicinity of the North Pole, from the old continents to the mainland of America, and there for a longer period retained its ancient appearance in the mastodons and horses.

There, as well as here, the present order of thingsthe cantonment of animals-has been in many ways determined and modified by mighty glacifications and prolonged periods of refrigeration. Hence the accordance of so many plants of the extreme north with Alpine plants after the Eocene vegetation had made its entry from the east. Since that age, the reindeer has been forced back to the north, and the musk ox has been expelled and exterminated from the Old World. The elephants, fleeing before the ice, have not returned; and the mammoth, immigrating with a rhinoceros from the north-east, has been destroyed with his associate. Others of his comrades, such as the primæval ox, died out only a few centuries ago as wild cattle; others, like the buffalo and the beaver, are nearly extinct as denizens of Europe; and others again, the deer and roe-deer, will perish with the forests and the game-laws. But of almost all the species of which we search for the extraction, Palæontology supplies us with the history and derivation; and in derivation we find the causes of geographical distribution sketched in vivid outlines.

XI.

The Pedigree of Vertebrate Animals.

THE final result towards which the doctrine of Descent directs its efforts, is the pedigree of organisms. To work it out is to collect the almost inconceivable profusion of facts accumulated in the course of about a century by descriptive botany and zoology, including comparative anatomy and the history of development, and to submit the existing special hypotheses to a minute scrutiny and renewed verification. We have therefore claimed in behalf of the doctrine of Derivation the privilege on which the progress of science generally relies that of investigating according to determined points of view, and accepting probabilities as truth in the garb of scientific conjecture or hypothesis. It is manifest that when the doctrine of Descent first made its appearance with the arguments proposed by Darwin, it was only possible to indicate the most general outlines of this great pedigree, which it was the special task of the new direction of science to demonstrate in all its details. But however and wherever specific research was attempted, either the results contributed the form of some part of the great pedigree, or there was, from the first, reason to pre-suppose certain kinships, and the