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or palæozoic formations, in which the terrestrial and fluviatile invertebrate fossils are equally wanting or scanty. The argument from the paucity of insects, and of fluviatile or land mollusks, seems to be on a par with the argument from the dredge.

• Tenthly,' continues our President, in opposition to the theory of successive development, in regard to the Palæontology of the tertiary periods, there seems to be every reason to believe that the orders of the mammalia were as well represented as now, and by species as highly organized, whether we turn to the lower, or to the middle, or to the upper eocene periods, or to the miocene or pliocene; so that during five or more changes, in this highest class of vertebrata, not a single step was made in advance, tending to fill up the chasm which separates the most highly gifted of the inferior animals and men.'

We can well conceive the general idea with which 999 readers out of 1000 will rise from the perusal of this statement in the Anniversary Address. It would be the reverse of the idea which would be conveyed by the statement that, during the tertiary periods, the species of mammalia successively perished, and were replaced by species more and more resembling those that now co-exist with man.

Supposing the latter statement to be true, whence then, it may be asked, the difference between the general idea it is calculated to excite and that imparted by the statement of the President of the Geological Society? It will be found to reside in the difference of the meanings which

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be attached to the words italicized in the three phrases as well represented,' . as highly organized,'' the most highly gifted. If an order of mammals be represented by any species in the eocene and pliocene strata, it may be loosely said, in respect of the organization of such order, to be as well represented in the one as the other : for the gradation is not very extensive in the range of a natural order of the mammalian class, Still it is something; and a baboon of the genus Macacus, in respect to its generic organization, does not so well represent the quadrumana as a tail-less ape of the genus Hylobates. If an order be considered as well represented according to the number of its representatives, then the quadrumanous one was better represented by the species of Hylobates, Semnopithecus, Macacus, and Callithrix of the later tertiary periods, than by the solitary Macacus of the earliest tertiary period. More Quadrumana may, of course, be hereafter discovered in the cocene formations, but we are concerned in testing the accuracy of the generalizations from the actually acquired facts.

The Edentata are a very remarkable and peculiar Order of mammalia. The first representative known in a fossil state is the Macrotherium Sansaniense, from the miocene of the Departe

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ment du Gers. Remains of the order became more abundant in the pliocene and post-pliocene strata ; and it is now represented by different genera and species in Asia, Africa, and America. It was not at all represented in any of the eocene periods. An edentate fossil may, perhaps, be hereafter discovered in one or other of the divisions of the eocene — but Sir Charles Lyell's statement in respect to the palæontology of the tertiary periods is absolute.

The Ruminantia form one of the most numerous, as well as the most valuable, of the existing Orders of mammalia. Not one fragment of a ruminant has hitherto been discovered in either the lower, or the middle, or the upper eocene periods. Ruminants first appear, but are scanty, in the miocene beds; they increase in number and in likeness to the actual forms, as the superincumbent strata approach those containing the remains and works of man, with whom the ruminants have so intimate a relation of subserviency. Here, then, is an order of the mammalia—and, according to Cuvier, the most natural order—not merely not so well represented in the earlier as in the later tertiary periods, but not represented at all in any of the divisions of the eocene period. In any of these divisions it is possible that the characteristic grinding-tooth or cannon-bone of a true ruminant may yet be discovered; but we find it difficult to understand why remains of that order should not have already occurred therein, as well as the bones and teeth of the strange non-ruminant herbivora of the eocene beds, if ruminants had been as well represented in the times of the palæotherium and lophiodon as at the present day. And we could have wished that the example of statements and arguments, the character of which it has been our duty to expose, had been offered to the young and ardent members of the Geological Society by any other than its President, who, by his position, as well as by his merited renown, is likely to sway the judgment with so much force.

With regard to the term highly organized-in relation to the theatre of life assigned to any mammalian species and the part

it had to play therein, such species was as perfectly and consequently as highly organized as it could be created ; it possessed all the gifts requisite for its well-being as such. If by high organization and gifts we are to understand an approximation to those of man, then two important steps have been made in advance, tending to fill up the chasm which separates the highest organized and most highly gifted of known pliocene or post-pliocene mammalia and man: those steps are represented by the species of the genera Pithecus and Troglodytes ; neither of which have as yet been found fossil.

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The facts of the succession and progression of the mammalian class in the five or more changes which it has undergone during the tertiary periods, already point to some generalizations of extreme interest; and it is much to be regretted that such indications should be hidden or set aside by inaccurate propositions, put forth to support a view of the uniformitarian character of the order of the development of the class on this planet. The researches of comparative anatomists have led them to certain conclusions as to a type or general pattern to which the varieties of structure in the existing species may be referred, and in respect to which type they offer different degrees of departure. Thus the typical number of the toes in the mammalia is assumed

7-7 to be five. The typical number of molar teeth =28, of which are premolars, dents de remplacement' of Cuvier,

molars, ' vraies molaires' of Cuvier. Canines and incisors are associated with these teeth, in both jaws in the typical dentition. Each tooth in this dentition and each toe can be traced from species to species, and indicated by a special name, or, as Owen has done, by a symbol.

The development of horns in the herbivorous quadrupeds is a departure from the general mammalian type for the special ends of the species possessing those weapons. So, likewise, is the diminution of the number of toes, either by non-development of one or more of the normal five, or by coalescence of those that are developed. The suppression or the excessive development of any of the teeth of the typical series is equally held to be a departure from the general type, and an assumption of a special organization,

În tracing the development of the existing mammalia, which all more or less depart from the ideal type, the embryos undergo change of form : they are not found in the Herbivora, for example, to be miniature rhinoceroses or bulls. Their acquisition of the characters of maturity is not by the evolution of previously existing structures, but by epigenetic addition, and by metamorphosis or by removal of parts. The young rhinoceros is without horns, has a smooth skin, and shows rudiments of incisors in those species which do not possess them in the adult (Owen's Odontography, p. 590). The young ruminant is likewise destitute of horns, has the two principal metacarpal and metatarsal bones distinct, and shows rudiments of canine and incisive teeth in the upper jaw, which are undeveloped and become absorbed as it grows older. The presence of such rudimental teeth, buried in the gums of the Rhinoceros bicornis,

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and of the horned ruminant, would be utterly unintelligble without the recognition of a type—and this recognition is the dawn of a species of knowledge respecting the laws of animal development which bids fair to transcend all the aspirations of actual physiology. But in what respect, it may be asked, does it relate to the question at issue touching the evidence to be derived from the tertiary fossil mammalia as to the truth or fallacy of the theory of successive development? We shall briefly cite the facts and leave the reader to judge.

The earliest Rhinoceros which has been discovered is from the Miocene strata of Epplesheim and of Sansan, department of Gers: it was called Rhinoceros incisivus by Cuvier, because it retained fully developed incisors in both jaws; it was called Acerotherium by Kaup, because it never developed its horn; and it has since been denominated Rhinoceros tetradactylus by Lartet, because it had four toes on each foot, instead of three, as in all the later species of rhinoceros. It will be seen that in all these characters, the Miocene rhinoceros adheres closer to the common type, and resembles more the embryo than the adult of the pliocene and existing species of rhinoceros. In the absence of horns, the presence of incisors, and in having the fourth toe on the fore-foot, the Miocene Rhinoceros also more resembled the Tapirotherium, its contemporary, than the modern Rhinoceroses do the modern Tapirs.

The Eocene herbivorous animals which most resembled the Ruminants are the Dicobune, Dichodon, and Anoplotherium. They were devoid of horns, had canines and incisors in the upper as well as the lower jaws, and had the two toes, answering to those that are soldered together to form common bones in the Ruminants, distinct-whence Professor Owen has compared them to the embryos of Ruminants.- British Foss. Mamm., p. 333.

The Palæotherium is an Eocene herbivore, with the typical dentition, and with three toes on each foot : it has some affinity with the existing tapir ; it has a closer one with the existing horsebut there is a wide interval between them. Compared with any known species of the genus Equus, the Palæotherium adheres much closer to the common Mammalian type, not only by having the toes answering to the second and fourth of the typical five functionally developed, but by retaining the first premolar in both jaws.

The Palæotherium of the Eocene period is succeeded in the Miocene by a species which departs so much further from the common type by the reduction in size of the outer and inner toes, that MM. Lartet and De Blainville have called it Palæotherium Hippoïdes. In the Miocene or Older Pliocene of Vaucluse chere occurs another species of tridactyle herbivore in which the

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outer and inner toes are so much more reduced, though still retaining their hoofs, and the form and proportions of the rest of the skeleton and the teeth are so much nearer those of the horse, that it has received the name of Hipparion from one Palæontologist, and of Hippotherium from another discoverer of it. In the strata unquestionably Pliocene are first found some remains of the true Equine genus-in which the second and fourth toes are reduced to rudiments of their metacarpals or metatarsals, called the splint-bones,' and which are concealed beneath the skin.

The huge proboscidian pachyderms are represented at the present day by the elephants of Asia and Africa. They are remarkable for the absence of premolars, for the large size and complexity of the true molars, for the absence of incisors in the lower jaw, and for the acquisition by the two incisors retained in the upper jaw of those enormous dimensions that obtain for them the name of tusks. This is a form of mammal that departs extremely in its dentition from the normal type. Some naturalists deem their peculiarities of such value as to make them a peculiar Order. But the Order or Family of Proboscidians had no known representatives in the Eocene tertiary strata. They are comparatively rare in the Miocene, and are most abundant in the newer Pliocene or Postpliocene strata.

In the Miocene age the Proboscidians are first represented by a species, which, from the comparative simplicity of its grinding teeth, is called Mastodon-and this mastodon (M. Simorrensis of Lartet) had two incisors in the lower as well as in the upper jaw, and had also premolar teeth in both jaws.*

Professor Owen has called attention to the prevalence of the normal or typical dentition in not only the herbivorous but the carnivorous mammals of the eocene and older miocene strata. It appears to have been the rule then; it is the exception now.

The above cited and other analogous facts indicate that in the successive development of the mammalia, as we trace them from the earliest tertiary period to the present time, there has been a gradual exchange of a more general for a more special type. The modifications which constitute the departure from the general type adapt the creature to special actions, and usually confer upon it special powers. The horse is the swifter by reason of the reduction of its toes to the condition of the single-hoofed foot; and the antelope, in like manner, gains in speed by the coalescence of two of its originally distinct bones into one firm cannonbone. Man, whose organization is regarded as the highest, departs

* Notice sur la Colline de Sansan, par Ed. Lartet. 8vo. 1851. † Art. • Teeth,' Cyclopedia of Anatomy, vol. iv., p. 853.

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