Comparison of the vital manifestations, or ac tions vegetables and animals.—In considering generally the manifestations of vitality in vegeta bles and animals, we immediately become aware of very distinct and peculiar tendencies in each class. A disposition to produce diversity of parts, and a symmetrical arrangement of these, are as striking features in the acts by which animals are evolved, as the opposite or a disposition to reproduce to infinity similar parts without sym metry is a character inherent in vegetables. The liver, spleen, heart, intestinal canal, pancreas, and vertebral column, are the principal asymmetrical parts in animals ; the organs of the senses, the lungs, kidneys, testes, ovaries, lateral bones of the head, and extremities, and the muscles, are the principal symmetrical parts ; and these seve rally cannot be said to be repeated,—they only exist in pairs, on either side of the mesial plane. Such accessory and unessential organs as hair, scales, feathers, &c. are the only ones that are found repeated among animals. The very opposite of this tendency prevails among vege tables; we find nothing like symmetrical ar rangement on either side of a middle plane, and we see the same parts repeated again and again to infinity, so that any single part, a branch, for instance, becomes an epitome of the entire tree.
Another peculiarity in the mode in which the vital processes build up vegetables and animals consists in the situation and disposition assigned to the various organs entering into their composition. Whilst in plants the whole of the organs destined to the manifestation of particular functions,—the leaves, flowers, sta mina, pistilla, roots, &c.,—are placed externally, and their interior or trunk is a mere prop upon which these parts are hung, in animals the whole of the essential organs destined for the preservation of the individual and continuation of the species are concealed, so that their ex terior is the shell, their interior the receptacle for the especial lodgement and protection of these.
Such diversity in the arrangement of the parts composing vegetables and animals does away with the necessity for the existence among the former of any thing like those central organs found in the latter, which, from the interior of the body, and generally from the mesial plane, send off radii of communication to every atom of the organization, and prove the media that unite their several and often widely separated parts into a whole. We discover nothing like prolongations from central organs—from a heart, an artery, a stomach, and a spinal cord or ganglionic system, among vegetables. lien ce the independence of the several parts of vegetables one upon another, hence their susceptibility of being multiplied by cuttings, and even of some species arising complete from their leaves.
A third and very important peculiarity in regard to the mode in which the vital processes are performed in the animal and vegetable kingdom is that many take place with con sciousness or knowledge of their occurrence, in the one, whilst they all occur unconsciously in the other. In vegetables the whole of the acts whose sum constitutes their vitality are perfectly irresistible, and take place in them without their knowledge, and uninfluenced by their will. A great many of the vital acts, in deed, take place without consciousness among animals also, such as the circulation of the blood, the digestion and assimilation of the food, &c., but the moment the animal passes
the sphere of its individual existence, whenever it has to act beyond itself, we find conscious ness of the action superadded to the capacity to act. The very lowest animals select their food, search for and appropriate their aliment as it presents itself to them ; the most perfect vege table, on the contrary, absorbs irresistibly., and without perception or will, the materials brought into contact with its roots in the earth, and its leaves in the air. The same wide differences are apparent in the act by which the species is continued : animals search for, and, by an inherent virtue denominated instinct, implying consciousness, distinguish the other individual of opposite sex, of which they have need in order to procreate their kind ; in vegetables, on the contrary, all is passive ; the pollen or fecundating powder is projected or falls upon the pistilium, or is even left to be brought into contact with this part by accident, without participation in the act, without consciousness of or will in its performance.
These two last named manifestations, the one subservient to the preservation of the in dividual, the other to the continuance of the spe cies, are accompanied with such circumstances in animals as presuppose in them other two peculiar faculties : these are perception and the power of locomotion. To preserve themselves as individuals and as species, they required powers which should make them acquainted with and enable them to establish relations between their own bodies and the world beyond them. By the faculty of perception, which may be taken as synonymous with sensibility in its widest acceptation, an animal is made aware of his individual existence, as well as of that of the material universe without him. This faculty also takes cognizance of all the internal sentiments, feelings, or desires of which by his constitution he is susceptible, and which are always in harmony with the part he is destined to play in creation. Sensibility may therefore be defined : the faculty by which impressions from without as well as sensations, emotions, and intellectual acts from Ns, ithin are perceived. The organ of this faculty is by universal con sent admitted to be the nervous system. The faculty itself, as the above definition indicates, is susceptible of being considered under two heads : as the impressions perceived or percep tions come from without, or as they emanate from within. The organs of the senses are the media through which external impressions reach the percipient principle which resides in the brain and medulla oblongata in the higher animals, the nervous ganglia in the lower, and these same parts are the instruments or elabo ratories of the internal sensations. Both of these kinds or modes of perception were alike necessary to the beings endowed with them. The external sensations are the watchmen of the system, admonishing animals of the pre sence of the objects they require for their pre servation ; the internal feelings, in like mariner, are centinels which admonish them of their wants and lead to the employment of the organs by which these may be supplied.