ANIMAL, one of the great classes of natural objects, generally defined an organized body, possessed of life, sensation, and the power of spontaneous motion. The branch of natural history relating to animals is denomi nated Zoology.
It might be expected, that a term so familiar, and sufficiently intelligible to the most illiterate, should be very easily defined ; but it has not yet been done satis factorily. Organization furnishes no decisive test, nor is life itself peculiar to this division of beings, for life is confessedly an attribute of vegetables as well as ani mals; and, with regard to sensation and the capacity of spontaneous loco-motion, there are strong resemblances of both in various genera of the vegetable kingdom. Boerhaave's mark of distinction, viz. the reception of nutrition mouth, has been rejected, because the nourishment of plants is also conveyed by instruments corresponding in their use, though dissimilar in struc ture. And, on the same principle, the criterion pro posed by others, the possession of an alimentary duct, or canal, has been considered insufficient.
The peculiarity generally fixed upon as characteristic of animals, is sensation. But it is difficult to determine what sensations are possessed by the,imperfect animals. Many living creatures appear to be endowed with the same number of sensitive powers, which we find in our own species; and with some of them, to a degree of acuteness and delicacy, to which we can form no pre tensions. We do not know that any animated being possesses a greater number ; but it is not at all impro bable, that some of the instincts which surprise us the most, may be modifications of sense, of which we are as incapable of forming any conception, as of the facul ties of superior beings. This, however, is mere con jecture. We are accustomed, with greater appearance of foundation, to consider many of the inferior tribes of creatures as being devoid of almost ever} sense, except touch. Here, too, it is possible we may be deceived. The organs of the different senses, in these imperfect creatures, may be diffused over their whole surface, or they may be constituted in some mode hitherto undis covered ; and it is highly probable, at least, that nature has made some provision for enabling them to select their food, and to relish the nourishment which they imbibe.
It is not at all necessary that we should be able to as sign some one specific difference, which marks the line of distinction between the constitution of plants and that of animals. All material objects possess certain corn mon attributes; and all organised substances, however various in texture and in qualities, are referable to a few general orders, which are observed to 'glide into one another, by gradations so slight, as to be almost un susceptible of description. Yet the discrimination be tween the functions of animals, and the laws of the vegetable economy, how strong soever may be the ana logies which prevail in these different departments of nature, is abundantly manifest for all the purposes of useful science. That spurious philosophy, which sig nalizes itself by the love of paradox more than by the love of truth, and which aims rather at puzzling than instructing, is held in deserved contempt by the man of common sense, as, instead of exalting the faculties, by sharpening them for discovery, it sinks its infatuated votaries below the level of the vulgar; and instead of extending the fields of knowledge, widens the bounda ries of ignorance.
It is unfortunate, that the barrenness of language should have so long operated to increase the difficulties of speculative men. The term, life, does not signify precisely the same thing when applied to vegetable and animal bodies. In both it is the principle which gives activity to the different functions, and at the extinction of which the process of dissolution commences. But the life of a plant and the life of an animal are as corn; pletely dissimilar as their configuration. Difficult as it may be to discover all the shades of difference, when we include the whole range of these two ample kingdoms, it is not, by any means, difficult to describe the differ ences between the more perfect animals and the more perfect vegetables. When we deScend to the produc tions of the lowest order in each, our inability to define the limits which separate the one from the other, pro ceeds from our ignorance of the nature of their func tions, which, in many cases, act so languidly, that we cannot detect their operation.