The object proposed in this paper is to notice, briefly, the various particulars in which animal beings are regarded by naturalists as most remarkably differing from those which possess the inferior organization of a vegetable, and to show that, in respect of each of these distinctions, exceptional instances occur in the case of some species, so that none of these are capable of affording grounds for an exact scientific definition between the two great kingdoms of organized nature, and that such a definition cannot be established.
1. The first points of difference mentioned as generally pevailing between plants and animals, were the evident particulars of form, size, and duration of existence. The animal usually presents a bilateral symmetry of form, being divisible along the median line into two halves of similar outline; and its limited number of similar organs and parts entirely differs from the complex and irregular branching of a plant. But, to mention no other exception to this general rule, the ramified form of Polypipheræ, entirely resembling that of a vegetable, though unquestionably possessing an animal nature, sufficiently shows that this ground of distinction is far from universal. In connexion with the more definite form of animals, may be noticed their more limited size and duration of existence. A forest tree may continue to live and flourish for centuries, gradually increasing in size throughout this long period; an animal, on the other hand, soon arrives at its full growth, and its entire existence is limited to a definite ...
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