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We have been speaking of similarities of organization, we have now to say something of the ordinations of division or distinction, by which certain animals, whatever may be the similarity of parts of their limbs or bodies, are arranged in broad manifest separation of distinct groups, so as to preclude the idea of any possible transition from one to the other.
In a popular view of the animal kingdom this would appear sufficiently plain in the most obvious examples, as, for instance, the distinction between the carnivora and the ruminants; for no one uninitiated in the mysteries of the Transmutationists could ever be brought to believe that a cow had, by any quantity of changes in her ancestors, proceeded from the stock which produced a tiger or a lion. But though this common sense view of the question of Dis. tinction of animals is really unanswerable, yet there are some other considerations of deeper moment that claim our attention.
Physiologists who have carefully studied organic beings, with a view to establish some fundamental system of arrangement, have observed these distinctions :
1. Creatures whose hearts are divided into four cavities, mammalia and birds.
2. Those having a heart consisting of three cavities, reptiles and amphibia.
3. Animals possessing a heart with two cavities, fishes and most mollusca.
4. Animals whose heart consists of a single cavity, articulated animals, worms, and insects.
5. Creatures in which the functions both of stomach and heart are performed by the same organ, as Medusæ.
This arrangement of the Animal Kingdom, in conformity with the structure of the heart, was proposed by the celebrated Hunter, and is here set before the reader that it may be perceived at a glance how formidable are the bar. riers which such divisions interpose to obstruct the scheme of Transmutation. In that theory there must have been a transference of life across these boundaries. If a reptile has, for instance, been converted, by Natural Selection and the Struggle for Life, into a bird, the animal with a heart of three cavities has, in its new form, assumed a heart of four ; its circulation has been altered, and the corpuscules of its blood changed in form : so also the fish has changed its heart to become a reptile, &c., &c.
The functions of the heart are in the closest connection with the organization and power of the animal, with the whole apparatus of its life; a fish could not, for a few minutes, exist with a heart different from that which Nature has bestowed on it; nor could a bird be a bird with the heart of a fish or a reptile.
As the reptile is supposed, in the School of Transmuta. tion, to be the antecedent and ancestor of the bird, we are to suppose that some time or other the change of structure
in this particular was effected, and that the transformed or transforming animal acquired, ready made, this new centre of its circulation suited for its new position in life. There could be no formation by gradual mutation of ages in this point. The reptile must have its peculiar heart, and so must the bird. “Slight modifications' are not admissible here. Life depends every minute on the action of the heart, there can be no empirical experiments here, po ‘slightly plastic' attempts at a new machine; to suppose an animal living with an intermediate heart for a million of years, must be too desperate a venture for the most ardent admirers of Natural Selection. That dextrous metaphor may be always on the watch to take advantage of the slightest beneficial change,' but it would soon be discovered that no change at all could be made, without destroying life, and utterly ruining the attempt at metamorphosis.
Therefore we say that a transition from a reptile with a tripartite heart to a bird with its heart of four cavities is impossible ; supposing we were to concede that the various genera and species of birds have slided into one another, that a blackbird may have had a common ancestor with a crow, and a goose have issued from a swan. This is not the question of the mutability of species, already discussed, but of a much wider separation, nature's grand organic distinctions in which, by a few settled arrangements of internal organism, certain animals are totally separated from one another in the scheme of life; but which, nevertheless, Natural Selection is supposed to have surmounted by those who adopt the theory of Transmutation.
The distinction of the structure of the heart, an efficient rule for dissociation and sejunction, answers well for a negative purpose; but for classification something more
precise is needed, and this has been effected by Cuvier, who looked more to the nervous system for an accurate distribution of the animal kingdom. Guided by this indicator he established his four divisions of Vertebrata, Mollusca, Articulata, and Radiata, and though these divisions, with the exception of the first, are named from their external appearance, the three first are defined by characters exclusively drawn from the internal organization. The nervous system is, in fact, “the essence and prime distinction of the animal' (Owen); its mind, so to speak, depends on this ; its peculiar character, the result of its sensibilities, is derived from the nervous centre and its ramifications; its body is constructed to suit the impulse of its will, and its will by the nervous system rules and directs the body.
The vertebrata rise in the comparative scale of existence through the peculiar arrangement of their nervous provision; Mollusca (oysters, &c., &c.) are obviously creatures of a lower life than the vertebrated fishes. In the Mollusca* the centres of the nervous system are sometimes disposed irregularly through the general cavity of the body, sometimes aggregated round the gullet, sometimes arranged with more symmetry along the abdomen, yet seldom better cared for or protected than the neighbouring viscera.
This provision, inferior and imperfect as it appears, compared with the nervous furniture of the vertebrata, is fully adequate for the wants and habits of those lower animals ; many of which can neither see nor hear, and have but little need of locomotion in the search for their food.
The nervous centres of the Mollusca consist of several detached masses placed in different parts of the body, without regularity of distribution or symmetrical arrangernent.'—Jones, 4.
When therefore life was to be exalted into a more vigorous manifestation, the vertebral column was formed, a case and protection for the nervous system, which as the spinal marrow, that mysterious albuminous electric pulp'(Owen). is there aggregated in force, and communicates with the citadel, the brain, shielded in another cavity, the skull.
Two strongly-built cavities, the vertebral column and the skull, protecting the nervous system, characterize the vertebrated* class; and this is wanting in all the inferior invertebrated animals. This is one of those great organic distinctions which bar a translocation of life from one class to another; any pretended transmutation here would be simply fabulous, as much as to pretend that a rock was changed into a tree.
“There can be no doubt,' says Professor Rymer Jones, that the nervous system must be regarded as the very essence of being of all creatures, with which their sensations, volitions, and capability of action are inseparably connected ; and such being the case it is a legitimate inference, that the capacities and powers of the several tribes are in im. mediate relation with the development and perfection of this supreme part of organization, and their entire structure must be in accordance with that of the nervous apparatus which they possess. The nature of the limbs and the external members, the existence or non-existence of certain senses, the capability of locomotion, and the means of procuring food, must be in strict correspondence with the powers centred in the nervous masses of the body, or in that arrangement of nervous particles which represents or replaces them.'
• Which consists of fishes, reptiles, birds, and mammals. The volume of the brain is proportionally larger as the animal occupies a inore elevated scale in the rank of life.