The next curious energy we meet with in organized nature, and which also equally belongs to animals and vegetables, is instinct. This I have defined to be "the operation of the vital principle, or the principle of organized life by the exercise of certain natural powers directed to the present or future good of the individual, or of its progeny." But what are these powers, with which the vital principle is thus marvellously gifted, and which enables it, under different circumstances, to avail itself of different means to produce the same end?

that directs plants to sprout forth from the soil, and expand themselves to the reviving atmosphere; fishes to deposit their eggs in the sands; birds in nests, of the nicest and most skilful contrivance; and the wilder quadrupeds to accomplish the same purpose in lairs or subterraneous caverns; that guides the young of every kind to its proper food, and, whenever necessary, teaches it how to suck? Are these powers also material, or are they immaterial? Are they simple properties issuing out of a peculiar modification of matter, or something superadded to the material frame?

In the confused language and confused ideas of various metaphysical hypotheses, and even of one or two that pretend to great exactness in these respects, instinct is made a part or faculty of the mind; and hence we hear of a moral instinct. But has the polype, then, or the hydatid, a mind? Are we to look for a mind in the midst of sponges, corals, and

* Vol. II. Ser. 11. Lect. IV.

+ Can that be a correct definition of instinct which embraces such a phænomenon as this?. ED.

funguses?—in the spawn of frogs, or the seeds of mushrooms? Instinct, however, the operation of the principle of life, equally superintending the entire frame, and every separate part of it, guiding it to its perfect developement, exciting its peculiar energies, remedying its occasional evils, and providing for a future progeny, is equally to be traced in all of them? Are instinct, then, and mind, the same thing? or is the vocabulary of the hypotheses I now advert to, and shall have occasion to examine more at large hereafter, so meagre and limited that it is necessary to employ the same term to express ideas that have no connection with each other, and which cannot, therefore, be thus expressed without the grossest confusion? It is high time to be more accurate, and to have both determinate words and determinate ideas; and it has been one object of this course of instruction to define what ought to be the real distinction between instinct, sensation, and intelligence.

But let us ascend a step higher in the great scale of life; let us quit the vegetable for the animal kingdom. If I take the egg or grain of a mustardseed, and the egg of a silk-worm, where is the chemist or physiologist that will point out to me the diversity of their structure, or unfold the cause of those different faculties which they are to evince on future developement and growth? At present, so far as they appear to us, they are equally common matter, actuated by the same common living principle, directed to different ends. To give them developement and mature form, we equally expose them to the operation of the sun and the atmosphere, and, in the case of the mustard-seed, of moisture: and

we are not conscious of exposing them to any thing else; all which, again, so far as we are acquainted with them, are nothing but matter in different states of modification. Yet the animal egg produces a new and a much higher power, which we denominate sensation, while the vegetable egg produces nothing of the kind. What is sensation, and from what' quarter has it been derived? Is it a mere property, or a distinct essence? Is it material, or is it immaterial?

This, also, has occasionally been called instinct, and been contemplated as of instinctive energy. With equal confusion it has also been called or contemplated as a property of mind. It is neither the one nor the other: it is equally different from both. We trace, indeed, its immediate seat of residence ; for we behold in the silk-worm a peculiar organ which does not exist in the mustard-plant, and to which, and which alone, sensation always attaches itself; and to this organ we give the name of a nervous system. But to become acquainted with he organ, in which sensation resides, is no more to become acquainted with the essence of sensation itself, than to know the principle of life because we know the general figure of the individual animal or vegetable in which it inheres; or than to know what gravitation is because we see the matter which it actuates.

As simple nerves, or a nervous cord, such as that of the spinal marrow, is the proper organ of sensation or feeling, the gland of a brain, from which the nervous cord usually, though not always, shoots, is the proper organ of intelligence; and as I had occasion to observe in a former study, when lecturing

VOL. III.

upon the subject of the senses, the degree of intelligence appears, in every instance we are acquainted with, to be proportioned, not, indeed, to the size of the brain as compared with that of the animal to which it belongs, as was conjectured by Aristotle, and has been the general belief almost to the present day, but as compared with the aggregate bulk of nerves that issue from it. * The larger the brain and the less the nerves, the higher and more comprehensive the intelligence: the smaller the brain and the larger the nerves, the duller and more contracted. In man, of all animals whatever, the brain is the largest, and the nerves comparatively with its bulk the smallest: in the monkey tribes it makes an approach to this proportion, but there is still a considerable difference; in birds a somewhat greater difference; in amphibials the brain is very small in proportion to the size of the nervous cord; in fishes it is a bulb not much larger than the nervous cord itself; in insects there is no proper brain whatever ; the nervous cord that runs down the back originating near the mouth; sometimes of an uniform diameter with the cord itself, and sometimes rather larger; and in infusory and zoophytic worms we have no trace either of nerves or brain.

In these last, therefore, it is possible, and indeed probable, as I have already observed, that there is no sensation: the vital principle, and the instinctive faculty, which is the operation of the vital principle, by the exercise of certain natural powers constantly appertaining to such principle, alone producing all the phænomena of life, as in plants.

* Vol. I. Ser. 1. Lect. xv.

In most insects, for the same reason, it is possible, and indeed probable, that though there is sensation, there is little or no intelligence: the brain, which is the sole seat or organ of intelligence, being totally destitute, in most of them, and of very minute compass in the rest. In fishes we have reason to apprehend different degrees of intelligence; in many amphibials somewhat more; more still in birds and quadrupeds, and most of all in man.

But what is intelligence, which is a distinct principle from sensation, and to which, as in the case of sensation, a distinct organ is appropriated? An organ, moreover, which, like that of simple sensation, may be also produced out of an insentient egg by the mere application, so far as we are able to trace the different substances in nature, of a certain proportion of heat; for the egg of the hen, unquestionably insentient when first laid, becomes equally hatched and endowed with the organs and properties both of sensation and intelligence, by the application of a certain portion of warmth, whether that warmth be derived from the body of the hen, of a dunghill, an oven, or the sun. But though we know the organ, what information does this give us of the thing itself? In what respect is intelligence connected with the brain? Does it result from its mere peculiarity of structure, secreted, like the blood, but of a finer and more attenuate crasis, or is it a something superadded to the organ? Is it matter in its most active, elaborate, and etherialized form, or is it something more than matter of any kind? and, if so, how has this superadded essence been communicated?

To this point we can proceed safely, and see