By the faculty of locomotion, again, an animal accomplishes all the promptings of his inward nature ; he places himself in relation with the beings and the things which he is ad monished by his instincts or internal faculties are necessary to him for his preservation as individual and continuance as species. Made aware of his wants by perception, by the faculty of locomotion he is enabled to minis ter to them. These two powers, let us ob serve, always exist together ; the one, indeed, necessarily supposes the other. Sensibility or perception is the monitor, locomotion the agent. Without perception locomotion could have sub served no end ; without some capacity of loco motion perception would have been a vain in heritance.
Vegetables evidently possess no power of locomotion analogous to that inherent among the higher animals,—where the seed falls there the plant springs, there it attains maturity, and there it dies. Neither do they manifest any thing like sensibility in outward act that can be ascribed to volition or consciousness : their nature, in fact, made perception unnecessary to them; and having no power of locomotion, it would have been useless in the two great acts by which organized beings minister to their pre servation as individuals and to their existence as species. Still it is impossible to deny every thing like capacity of outward motion to vege tables. Although they have no power of trans porting themselves over the surface of the earth or through its waters like animals, many of them exhibit motions in their leaves and flowers in relation with the state of the atmosphere, and the diurnal revolution of the earth ; the sexual organs in several species move the one towards the other ; and about the foot-stalks and petioles of the mimosa pudica and other plants we observe particular organs that con tract when stimulated, very much in the same way as the muscular fibre among the higher animals. Moreover, the motions by which the radicle constantly seeks the ground or tends downwards and the plumula shoots into the air, that by which some of the higher phano gamous plants twist in spirals around objects near them, and by which all preserve one side of their leaves towards the light, cannot be held as accidental or merely mechanical acts. Seve ral genera of the confervm and tremellm even exhibit such remarkable oscillatory movements as have induced different naturalists and phy siologists to reckon them among the number of the animals.
With all this, however, locomotion among vegetables is a very limited power contrasted with the faculty among animals. These exhibit all the automatical motions of vegetables, and have in addition a particular system, the mus cular, superadded to their organization, by which many of the most important offices of the eco nomy are performed : not only instrumental in procuring the food by which they are main tained, but in putting into play the digestive and respiratory apparatus by which the nutri tive juices are prepared and assimilated, and finally distributed among the higher tribes to every part of the body. The existence of this system is in fact one of the grand characteristics of the more perfect animals. By its means they react upon the external world and modify it according to their wants ; by its means they guide their senses and enlarge the sphere of their acquaintance with things beyond them selves ; by its means they impress the air with the tones and articulate sounds, or execute the signs by which they make known the various states of their affective or moral and intellectual being to one another ; finally, by its means the sexes approximate, and those acts take place which lead to the engenderment of new indivi duals and the continuance of species.
The best informed among physiologists, how ever, do not confine the motions of all animals to the act of the particular tissue we denominate muscular. The polypes and many even of the massy acalephs, to say nothing of the smaller infusories, rotifers, &c. though they move freely, cannot be shown to possess muscular fibres in their constitution; neither indeed can any nervous system, upon which muscular contractions and voluntary motion have always been held dependent, he demonstrated in these creatures. It is consequently probable that the means by which spontaneous motion takes place in these lower animals are peculiar, as indeed we must acknowledge the evident mo tions which occur under many other circum stances in the world of organization to be.
But let us now turn to the special manifesta tions of vitality of the two great classes of organized beings we are engaged in examining. These we shall consider in the following order, which is also that we have adopted in contrast ing the manifestations of activity of unorganized and organized beings,—namely, origin or repro duction, nutrition or self-preservation, changes