wishes to ascertain the solidity of an object within his reach, he knows that he has but to stretch forth his hand, and to feel in what degree it resists the pressure he gives it. No exertion even of this kind is required for hearing the voices of his companions, or for being apprized of the pealing of the distant thunder. Yet how much is really implied in all these apparently simple phenomena. Science, we see, has taught us, that these perceptions, far from being direct or intuitive, are only the final results of a long series of operations, produced by agents of a most subtile nature, which act by curious and complicated laws, upon a refined organization, disposed in particular situations in our bodies, and adjusted with admirable art to receive their impressions, to modify and combine them in a certain order, and to convey them in regular succession, and without confusion, to the immediate seat of sensation.

Yet this process, complicated as it may appear, constitutes but the first stage of the entire function of perception; for, before the mind can arrive at a distinct knowledge of the presence and peculiar qualities of the external object which gives rise to the sensation, a long series of mental changes must intervene, and many intellectual operations must be performed. All these take place in such rapid succession, that, even when we include the movement of the limb, which is consequent on the perception, and which we naturally consider as part of the same action, the whole appears to occupy but a single instant. Upon a careful analysis of the phenomenon, however, it has been found that no less than twelve distinguishable kinds of changes must always intervene, in regular succession, between the action of the external object on the organ of sense, and the voluntary movement of the limb which it excites.

The external agents capable of affecting the different parts of the nervous system, so as to produce sensation, are of different kinds, and are governed by laws peculiar to themselves. The structure of the organ is accordingly adapted, in each particular case, to receive the impressions made by such agents, and is modified in exact con

formity to the laws they obey. Thus the retina is adapted to the action of light, and the various parts of the eye through which the rays pass, before reaching the retina, are constructed with strict regard to the laws of optics. In like manner, the ear is so formed as to receive delicate impressions from those vibrations of the air which occasion sound. The function of each nerve of sense is determinate, and can be executed by no other part of the nervous system. The functions are not interchangeable, as is the case with many others in animal life. No nerve but the optic nerve, and no part of that nerve, except the retina, is capable, however impressed, of giving rise to the sensation of sight;* no part of the nervous system, but the auditory nerve, can convey that of sound. And so with the three other senses. There is a peculiar set of nerves for tasting, another for smell, and another still for touch.

What is further worthy of remark, is, that, in almost every case, the impression made on the sentient extremity of the appropriate nerve, is not the direct effect of the external body, but results from the agency of some intervening medium. There is always a portion of organic matter interposed between the object and the nerve on which the impression is made, so that these never come into direct contact. This is true even in the case of touch, where the organ is defended by the insensible cuticle, through which the impression is made, and by means of which, it is duly modified. In the organs of taste and smell, too, the same observation applies, the nerves of these organs being not only defended by the cuticle, but secured from too violent action, by a secretion expressly provided for that purpose. In the senses of hearing and vision, the changes which take place in the organs interposed between the external impressions and the nerves, are still more remarkable and important. The objects of these senses, as well as those of smell, being situated at

*[This seems to be too absolute a statement; for there are certain impressions connected with dreaming, disease, &c., which require its modification. But this is no place to enter on so metaphysical a subject.-AM. ED.]

a distance, produce their first impressions by the aid of some medium, exterior to our bodies, through which their influence extends. Thus the air is the usual medium through which light, sound, and odor are conveyed to their respective organs. The physical laws which regulate this medium, as well as those which belong to the agents themselves, must therefore be taken into account, before we can fully understand the phenomena of sensa

tion.

We have thus before us, a most complicated system of contrivances and adaptations, which meet us on every side, and are full of instruction. Whether we consider the peculiar laws of the external world, by which they are fitted for the conveyance of the various sensations,—the laws of solid and liquid bodies, of sound, of light, of odoriferous effluvia, of the atmosphere; or regard, in the organization of living bodies, the nerves of feeling, of taste, of smell, of hearing, and of sight, with the beautifully-constructed mechanism, by means of which these nerves are enabled to perform their functions; or examine the nice adjustments by which such various and naturally distinct and unconnected objects are made to harmonize, coalesce, and cooperate, in producing the desired results; or, finally, attend to the nature of these results, as relates to the existence and happiness of sentient beings, we are at a loss what to admire most, and are irresistibly led to acknowledge and adore, in them all, the work of a Being transcendent in every conceivable perfection.

FIFTH WEEK-FRIDAY.

OF THE ARGONAUT AND NAUTILUS.*

6

HAVING, in the Winter' volume, considered animals in their dormant state, and, in that of Spring,' described

*It may be proper, once for all, to acknowledge that I am chiefly indebted for the facts in natural history, of which I have made use in

their reproductive powers and instincts, it is my intention now to give some account of their faculties, qualities, and actions in their full developement, proceeding according to the plan I have uniformly adopted, and selecting such remarkable cases, in the various genera, as may serve best to illustrate the perfections and modes of operation of the Creator.

"The bed of the mighty ocean," says Kirby, "is not only planted with a variety of herbs, which afford pasture to many of its animal inhabitants; but it has other productions, which represent a forest of trees and shrubs, and are, strictly speaking, the first members of the zoological world, connecting it with the vegetable. These are denominated Zoophytes, or animal plants, and Polypes. This last name has been adopted from Aristotle; with him, however, and the ancients, it is evidently used to designate the Argonaut and Nautilus of the moderns, and also to include some terrestrial shells. The zoophytes are not confined to the ocean; every rivulet, and stagnant ditch, or pool, affords to some kinds, most commonly denominated Polypes, and also to some sponges, their destined habitation. An infinite army of shellfish, whether multivalve, bivalve, or univalve, also cover the bed of the ocean, or move in its waters; and some dance gayly on its surface with extended sails or dashing oars, when tempted by fair weather."

Contenting myself with this general account of the inferior inhabitants of the ocean, I shall select only two species of this class for particular description, the first of which, shall be taken from the tribe last alluded to; I mean that of those which "dance gayly on the surface of the ocean, with expanded sails and dashing oars."

There are several kinds of shell animals, which use the apparatus Nature has bestowed on them, to navigate the

the following papers, to Goldsmith's Animated Nature, the Bridgewater Treatises of Mr. Kirby on habits and instincts, and Dr. Roget on physiology, and to the works on Insects, Birds, &c., published in the Library of Useful Knowledge, as well as to the posthumous work of Dr. Macculloch, on the Attributes of God, published while this volume was preparing for the press.

surface of the ocean. Of these are a few species of molluscans; but there are two families, whose formation and habits demand particular notice, I mean those of the Argonaut and Nautilus. These creatures belong to an order called Cephalapods, because their feet are placed in the same part of their bodies as their head. The various species of this class are remarkable not only for their organization, form, and habits, but for their position in the animal kingdom. In their composition, they seem to include elements from both the great divisions of that kingdom; from the vertebrates, the beak, the eye, the tongue, an organ for hearing, the crop, the gizzard, and an analogue of the spine, with several other parts enumerated by Cuvier; and from their own sub-kingdom, many of their remaining organs. We may descend to the very basis of the animal kingdom, for this first draught of the animal system; the sucker-bearing arms, seem to have their first outline in the fresh-water polypes; the lamellated tentacles, above and below the eyes, appear to lead to the antennæ of crustaceans and insects; and the numerous molluscan characters are obvious to every one. At the same time, this singular creature exhibits many characters, both in its most extraordinary outward form, and in its internal organization, that are quite peculiar, and of which no animal, at present known, exhibits the slightest traces; I need refer only to its muscular apparatus, adapted to its unparalleled form; its system of circulation, carried on, in the first order, by three distinct organs instead of one heart; and the wonderful complication of their tentacles, of the nerves that move them, and the vascular system that animates them.

This description, which I have considerably abridged from Mr. Kirby's account, shows a remarkable peculiarity in the class of animals to which the species we are considering belongs. They have each, also, peculiarities of their own; but they agree in one particular, that they each use their shells as boats, in which they transport themselves across the surface of the sea, erecting their sails to the wind, and plying their oars, as if they were the prototypes of the sailor and his vessel, with which