THE Connection between the animal and the external world is maintained by means of the several senses.

Whatever may be its natural desires and wants, these are necessary in order to their gratification. Their number and degree of perfection will correspond to the necessities and the situation of each individual. The animal which does not voluntarily seek its food needs not sight; the animal which cannot fly when pursued needs not to hear. There is the same harmony of relation between the senses and the powers called into action by them, that has already been pointed out between other circumstances in the structure of animals and the condition in which they have been placed. None have appetites or wants which there is not a provision for their indulging, and indulging with a certain degree of safety. There is always a correspondence, for example, between the appetite that suggests a particular kind of food, the senses that perceive it, the limbs which procure it, and the organs by which it is digested.

It makes no difference as to the number and perfection of the senses required, whether the presiding principle with which they are connected be intelligence or instinct. It has been argued that the wonderful operations brought about by certain animals, insects particularly, are not to be attributed chiefly to instinct, because, were they owing to a principle so mechanical, they would not require organs of sense so delicate as those they possess. "If," says a writer on this subject, "insects in all their actions were directed mainly by their instinct, they might do as well without sight, hearing, smell, and touch." It might as well be urged that they could do without limbs, antennæ, mouth, and other external organs. But in truth the nature of the internal principle has nothing to do with that of the organs by which it is administered. It makes no difference in the bee, for example,

whether it be induced to build its cell and provide its food by a blind instinct or a reasoning intelligence, so far as the organs by which it acts are concerned. In either case it requires organs of taste to perceive, as well as organs of motion to procure, the necessary materials; organs of touch to take note of the progress of its work as it goes on, as well as organs of motion to carry it on. The number and degree of perfection of the external senses are always strictly in proportion to the wants and desires of the internal governing principle, whatever that may be.

No animal possesses more than the five senses of sight, hear ing, smell, taste, and touch; many are deficient in some of them, but none in all; and we may be sure that every one possesses all that are essential to the condition of existence in which it has been created.

In the lowest of the Radiata it is probable that there exists only a vague and indistinct perception of the qualities of external objects. Their senses may be resolved into a certain degree of feeling, or touch. We can hardly attribute to them either of the others distinctly, yet this one sense appears to be so modified as to be capable of performing some of the offices of the others. Their feelers or tentacula, for example, can determine whether the object which they encounter in the water is fit for their food. Touch them with a stick or the finger, and they shrink from it. Let them be touched by a worm, and they immediately grasp it and convey it to the mouth. This implies something of the attributes of smell and taste. So, too, they are influenced by light, and by those vibrations which constitute sound; and thus in a certain limited way they are influenced by the causes which -excite all the senses. We cannot say that they have smell, taste, hearing, or sight, yet the sense of feeling is so modified as to perform, as far as it is needed, the office of them all.

As we ascend in the scale of being, the senses of smell and taste become more distinct from that of feeling, but it is not til' we arrive at the highest species among the Articulata and Mol lusca that we find them entirely distinct. Here, too, we first perceive the existence of the superior senses of sight and hearing. It is to be remarked that these, which furnish the only very distinct information concerning objects with which animals are not

in contact, are usually accompanied by a considerable capacity for motion from place to place. It is true that smell, also, may give information relating to bodies not in contact; but this information is not of a very exact nature, and does not relate to objects at any considerable distance, except in those species which possess also sight and hearing.

In some of the Mollusca, the snail for example, a rude organ of sight is detected. Hearing is probably also present, but as from the nature of the vibrations on which it depends, an external organ is not necessary for its exercise, we cannot point out its seat. In the cuttle-fish the organs of these two senses become more distinct, and they are accordingly capable of free and rapid motion from place to place.

In Insects there are found increased and varied powers of motion, accompanying increased powers of sense. But with partial exceptions it is only in the vertebral animals that all the senses are found exercised by organs of determinate place and

structure.

Every part of every animal which is organized is capable, under some circumstances, of being influenced by the contact of external bodies. This general sense of feeling resides in every part, but it is only when exercised by particular organs, and in a peculiar way, that we give it the name of touch. An animal may live, and exercise its necessary functions, with this sense only. This is not true of any other. No animal can do it by means of any other single sense.

But although every part feels in this general way, the skin, in the higher animals at least, is the organ in which the ser.se especially resides. That modification of it which we call touch is still more limited in extent, whilst the information it gives is far more definite. Feeling acquaints us merely with the presence of bodies; by touch we acquire a knowledge of some of their qualities. Touch is the sense of feeling in an active state; and it becomes active chiefly by the form and relation of the organs in which it resides. When an external body is touched by a single plain surface, like the extended surface of one of the limbs, the cheek, or even the palm of the hand, we merely perceive its presence, its temperature, perhaps its hardness, and some other

very general qualities. But when it comes in contact with two or more surfaces, as the lips, the tongue, the fingers, then some of its properties, especially its shape, regularity of surface, &c., may be perceived. The nicety of touch depends upon the number of distinct impressions which we can receive and compare together. If we touch a body in its different parts with the tip of a single finger many times, we get a less accurate idea of its figure and dimensions than when we grasp it but for a single moment with the whole hand, because the connection and relation of the impressions are of more importance than their number. This makes the hand of man the most perfect organ of touch in nature, though perhaps, for certain limited purposes, we may find its equal in some of those organs of insects by which their wonderful operations are carried on.

Next to the hand of man come those of the monkey tribe and the trunk of the elephant. In all of these is perceived the same characteristic of structure which gives its excellence to the hand of man, but in a less perfect degree.

In departing from man, we trace a gradual variation in the structure of the anterior extremity, till, in the complete quadrupeds, it becomes a mere organ of motion. Precisely in proportion as it becomes an instrument of motion, it ceases to be an organ of sense; so that the parts corresponding to those which in man are gifted with that delicate sensibility and exquisite discrimination characteristic of the human hand, in the ruminants and in the horse kind have degenerated into an insensible hoof, fit only to aid the animal in its progression. But there is in this case some compensation. In our own species, when one sense is blunted or obliterated, the others become more acute; and so in animals, in proportion as the sense of touch is lost by the diversion of their extremities to other purposes, it is either transferred to other parts, or the other senses become more acute. Man, whose touch is so nice, lacks nicety of smell and taste. The degree in which these senses are possessed is indicated by the size and structure of their organs. Hence, as they reside in the face, in man the face is small compared with the head; the nose and mouth do not project; but as we descend through the apes and the carnivora to the more complete quadrupeds, these parts do project, and the

fore limbs deteriorate till we finally find them terminating in hoofs.

The only parts, in complete quadrupeds, which are possessed of a nice sense of touch, are the extremity of the nose and lips, and the tongue. This is the more necessary to them because the lips answer with them the same purpose that the fore limbs of other animals do, namely, to seize their food. This relation is strikingly illustrated in some animals, where a peculiarity of structure is required. Thus the elephant, not being able to take food into his mouth by his lips, has their nice sensibility carried out to the extremity of the trunk, where, as in the nose of other quadrupeds, the senses of smelling and touch are united just where their united function is required.

One of the most singular exercises of sensibility is that which has been noticed in the bat, when deprived of its sight, even by the entire destruction of its eyes. Spallanzani, observed that when some of these animals were confined in rooms opening into each other, they continued to pass through the door, while on the wing, with the same facility as when possessed of sight. Suspecting this might be the result of habit, willow rods were placed perpendicularly in different parts of the rooms, and their position was from time to time changed; yet the animals still flew freely around, avoiding the ceiling, the walls, the door, and the rods, precisely as if they had continued the exercise of sight. It seems impossible to attribute this singular phenomenon to anything but an exquisite sense of feeling, probably existing in the extended membrane of the wings.

In Birds, Reptiles, and Fishes, the sense of touch is very confined, as is obvious from the very structure of their bodies; whilst in Insects it assumes an importance but little if at all inferior to that which it has in man himself.

The sense of taste is in some respects nearly related to that of touch. Both require that the object should be brought into contact with the organ. But they are intended to inform us of qualities of a different kind; namely, touch, of the physical and mechanical; taste, of what may be called the chemical, qualities of bodies. In order to taste, it is necessary there should be a solution of the body tasted; and accordingly where this sense is