ase elongated, and pointed at their extremities; loricated, or mailed, when the body is inclosed in a hard, callous, or bony integument, or in scales so closely united as to seem but one; fasciated, or banded, when marked with transverse zones, from the back to the belly; striped, when marked with very narrow, scattered, and coloured streaks; vittated, when marked with longitudinal zones along the side, from the head to the tail; reticulated, or chequered, when marked with lines forming the appearance of net work; pointed, or dotted, when marked with points, either longitudinally disposed, or without order; and variegated, when of different colours.

The head is always placed at the anterior part of the body, and reaches from the extremity of the nose to the gills. The head contains the mouth, nose, jaws, lips, teeth, tongue, palate, nostrils, eyes, branchial opercules, the branchiostegous membrane, the aperture of the gills, and the nape. The branchial opercules are scaly, or bony processes, situated on both sides of the head, behind the eyes, closing the aperture of the gills, and sustaining the branchial membrane. The branchial, or branchiostegous membrane, is a true fin, formed of cartilaginous crooked bones, joined by a thin membrane, lurking under the opercula, to which it adheres, and is capable of being folded, or expanded, as necessity requires.

The trunk is that part of the body which extends from the nape and branchial aperture to the extremity of the tail. It comprehends the gills, throat, thorax, back, sides, abdomen, lateral line, anus, tail, and scales. The gills, or branchia, consist, for the most part, of four crooked, parallel, unequal bones, furnished on the outer, or convex part, with small soft appendages, like the beards of a feather, and generally of a red colour.

The fins consist of several rays connected by a tender film, or membrane; and they are raised, expanded, or moved, in various directions, by means of appropriate muscles. The rays of the fins are either jointed and flexible small bones, whose extremity is often divided into two parts, or hard and prickly, without division at the extremity. In some cases, those on the back of the fish are furnished with membranaceous appendages, simple, or palmated, and adhering to the apex, or sides. The fins, according to their position, are denominated dorsal, pectoral, ventral, anal, or caudal.

of bones which constitutes the frame-work of its body. The number of these bones is not uniform in each individual, but varies according to age and species. They may be conveniently divided into those of the head, thorax, abdomen, and fins.

The muscles are an assemblage of small bundles of fleshy fibres, partly red, and partly whitish, enveloped in a common membrane. The first of these is called the fleshy portion of the muscle; the second the tendon. Each muscle thus composed, is susceptible of contraction and dilatation. The former is accompanied by a visible swelling, hardening, wrinkling, and shortening of the muscle, and the latter by its elongation, expansion, and recovery of its former softness and flexibility. Its force, in general, depends on the quantity of fibrous matter which enters into its composition, and its moving power on the length and size of the fibres.

The brain of fishes is a very small organ relative to the size of the head. It is divided into three equal lobes, of which the two anterior are contiguous; the third being placed behind, and forming the cerebellum. These three lobes are surrounded by a frothy matter, resembling saliva. In this region the optic and olfactory nerves are easily discovered.

The swimming, or air bladder, or sound, is an oblong white, membranous bag, sometimes cylindrical, sometimes elliptical, and sometimes divided into two or three lobes, of different lengths. It is usually situated between the vertebræ and the stomach, and included within the peritonæum. In some fishes it communicates with the stomach, and in others, with the oesophagus. The flat fishes are unprovided with this organ.

The intestines, which in man are placed transversely, have a longitudinal position in fishes, and are all connected with the substance of the liver. They are in general very short, making only three turns, the last of which terminates in a common outlet or vent. The appendices, or secondary intestines, are very numerous, composing a groupe of worm-like processes, all ultimately terminating in two large canals, opening into the first intestine, into which they discharge their peculiar fluid. We shall, under the word PISCES, give an account of the several functions peculiar to this class of animals.

ICHTHYOPHTHALMITE, in mineThe skeleton of a fish is the assemblage ralogy, a stone found in Sudermania, of a

ICONOCLASTS, in church history, an appellation given to those persons who, in the eighth century, opposed image-worship, and is still given by the Church of Rome to all Christians who reject the use of images in religious matters.

ICOSAHEDRON, in geometry, a regular solid, consisting of twenty triangular pyramids, whose vertexes meet in the centre of a sphere, supposed to circumscribe it; and, therefore, have their height and bases equal; wherefore the solidity of one of those pyramids multiplied by twenty, the number of bases, gives the solid content of the icosahedron. See BODY.

ICOSANDRIA, in botany, the name of the twelfth class in the Linnæan system, consisting of plants with hermaphrodite flowers, furnished with twenty or more sta mina, that are inserted into the inner side of the calyx, or petals, or both. By this last circumstance, and not by the number of stamina, is this class distinguished from the class polyandria, in which the number of stamina is frequently the same with that of the plants of the class icosandria, but they are inserted, not into the calyx or pe tals, but into the receptacle of the flower. The icosandria furnishes the pulpy fruits that are most esteemed, such as apples, plumbs, peaches, cherries, &c. whereas the polyandria are mostly poisonous, as the aconite, columbine, larkspur, hellebore, and others. The species of the icosandria have a hollow flower cup composed of one leaf to the inner side of which the petals are fastened by their claws. In this class there are five orders, founded upon the number of the styles or female organs. The myr tle, almond, and plumb bave a single female organ; the wild service, two; the service and sesuvium, three; mediar and apple, &c. five; rose, raspberry, strawberry, &c. an indefinite number.

IDENTITY, denotes that by which a thing is itself, and not any thing else; in which sense, identity differs from similitude as well as diversity. The idea of identity we owe to that power which the mind has of comparing the very being and existence of things, whereby considering any thing as existing at any certain time and place, and comparing it with itself as existing at any other time and place, we accordingly pronounce it the same, or different. Thus, when we see a man at any time and place, and compare him with himself when we see him again at any other time or place, we pronounce him to be the same we saw before.

To understand identity aright, we ought to consider the essence and existence, and the ideas these words stand for; it being one thing to be the same substance; another the same man; and a third, the same person. For, suppose an atom existing at a determined time and place, it is the same with itself, and will continue so to be at any other instant as long as its existence continues; and the same may be said of two or any number of atoms, whilst they continue together; the mass will be the same; but if one atom be taken away, it is not the same mass. In animated beings it is other. wise, for the identity does not depend on the cohesion of its constituent particles, any kow united in one mass; but on such a disposition and organization of parts, as is fit to receive and distribute life and nonrishment to the whole frame. Man, there. fore, who hath such an organization of parts partaking of one common life, continnes to be the same man, though that life be communicated to new succeeding particles of matter vitally united to the same organized body; and in this consists the identity of man, considered as an animal only. But personal identity, or the sameness of an intelligent being, consists in a continued con sciousness of its being a thinking being, endowed with reason and reflection, capable of pain or pleasure, happiness or misery, that considers itself the same thing in different times and places. By this conscious. ness every one is to himself, what he calls self, withont considering, whether that seif be continued in the same or divers substances; and so far as this consciousness extends backward to any past action, or thought, so far extends the identity of that person, and makes it the object of reward and punishment. Hence it follows, that if the consciousness went with the hand, or

any other limb, when severed from the body, it would be the same self that was just before concerned for the whole. And if it were possible for the same man to have a distinct incommunicable consciousness at different times, he would, without doubt, at different times make different persons; which we see is the sense of mankind as to madmen, for human laws do not punish the madman for the sober man's actions, nor the sober man for what the madman did, thereby considering them as two persons.

We

IDEAOLOGY. The philosophy of the human mind. We are conscious of our own existence; and in this consciousness we perceive a certain variety or successive change, which we distinguish by the name of thought. It seems as if it would be a vain attempt to investigate by what physi cal operations the proceedings of the mind may be caused, supported, or governed. The primary objects of thought are derived from our sensations or perceptions. can form no conception of any subject of thought which shall not be referable to the senses. During the actual time of sensation we suppose ourselves to be operated upon, by some beings or objects which constitute no part of ourselves; and we do not hesitate to infer from those sensations, that an external universe does actually subsist. Berkeley, Hume, and others, have made this a subject of question; and it must be confessed, that we have no absolute proof respecting it. From the certainty, however, that we ourselves do not cause the changes which produce sensation in us, we are irresistibly impelled to an affirmative decision of this question; which after all seems neither important nor useful, more especially when we consider that the same uncertainty pervades all our researches, whenever we refine so far as to treat of subjects which are not referable to cause and effect.

In many instances, the sensations we experience afford some resemblance of the objects which cause them, as in the figures of bodies; but in others, it is probable that no such resemblance exists, as in colours, sounds, &c. A distinction has therefore very properly been made, between that which is perceived, and the cause of the perception; and, moreover, as we find that effects, similar to our antecedent perceptions, may and do take place, though the organs of sense are not then acted upon, we make a further distinction between VOL. III.

these last, and the perceptions themselves. We call them ideas. They not only resemble the perceptions, as individually consi dered, but likewise make their appearance in the same arrangement or order of recurrence. We think we perform a positive act, in many instances, in bringing them forward, which we call an act of the memory, or recollection; and their concomitant appearance, or the succession of ideas by recollection, in the similarity or the order of the sensations, has been called the association of ideas. The same term is likewise applied, when we speak of the recurrence, in idea, of an entire contemporaneous sensation, in consequence of part of it being brought forward in the memory.

Much discussion has taken place among philosophers, respecting the origin and nature of our ideas; in which it must be confessed that a mis-application of terms, a confusion of intellectual research, with an admixture of theological notions, and seve ral other causes, have united to render a plain subject considerably obscure, even in the hands of men of much talent and acuteness. In particular, it has been a subject of controversy, whether man possesses innate ideas. If an idea be the recollected picture of a sensation, we must surely date the possession of ideas from the earliest period of the existence of an animal; and it seems absurd to deny to the embryo, before birth, a consciousness of the voluntary power it exerts in muscular motion, or a power of feeling, and perhaps of being affected by sounds :--but without indulging any wildness of conjecture, are we not compelled,-when we see an animal in the first hour after its birth, seek the breast by the act of smelling, follow a visible object with its eyes, and alter the adjustment of their axis according to the distance of that object; when the same infant being set upon its feet, immediately and correctly makes the motion of jumping,-are we not compelled to admit, as incomparably the greater probability, that these powers have subsisted, though not exercised, in the fœtal state, rather than that they should have been created at the instant of its birth? This then is our situation with regard to innate ideas, and it would be a contradiction in terms to speak of innate notions or principles. Those deductions of fitness to an end or purpose, which constitute principle, certainly cannot be made till after the requisite propositions have been presented or N n

have occurred to the mind. Previously to this, the conscious being may be said to possess the capacity to perceive and to deduce relations; and it seems of very little consequence whether we call this capacity innate or not.

We are so constituted that most of our sensations give us either pleasure or pain; and whenever these are vivid, we are put into a situation of mind respecting them called desire; namely, for the continuance or return of the pleasurable sensations, and for the cessation, or absence, of those that are painful. These desires, in their various modifications and combinations, are distinguished by the general name of the passions. Whenever they are strong and urgent, they engage the mind so fully, that the ordinary, association of ideas, and the regular processes of reason become obscured, interrupted,or suspended. A continuance of this state, as when the passions are exalted by disease, is called insanity; and in all states of passion man is more or less insane.

None of our sensations are simple, and consequently none of our ideas can be so. All sensations consist of parts, representing parts of the objects perceived, whether contemporaneously or in succession; and we are also capable of receiving two or more sensations at the same time. Whether the difference between one sensation and another may arise merely from the relations of their own parts with respect to each other, or from any other causes, is not of importance to be discussed in this place; but it is certain that we are greatly interested in observing these relations. Thus we take no tice, that one thing is greater or less than another; that in figure, position, duration, and other affections, they are not the same; and that certain changes in inanimate, as well as in conscious beings, are without exception followed by other changes, from which we are led to expect and to foretel events. This last class of observations establishes the doctrine of causes and effects; and a large part of our lives is employed in determining the order of these successions.

(which are ideas considered in succession) it constitutes truth; if otherwise, it is falsehood.

Among numerous other inaccuracies which tend to mislead in the investigation of ideaology, a principal one is, that the term idea has been confounded with that of notion. Notions always grow out of the relations of ideas, and they always imply comparison. When the notion or thing asserted, agrees with the ideas or events,

Our sensations in every case, without exception, afford no more than a partial indication of the nature of the objects which cause them. We cannot see the whole of an animal, but only one side, and that very imperfectly; so that the ordinary visible perception of a horse would be the same, whether its hair were long or short, its eyes imperfect or the contrary, &c. and the recollection, or idea, of that individual horse would be still more imperfect, by the omission of particular variations or spots of colour, or other subordinate objects; which, though they may have existed in the sensa tion, have not remained in the memory. Thus it is, from the nature of things, that some part of the sensations will be abstracted, or left out in the idea: and if in reasoning upon that subject, namely, the horse, a comparison were to be instituted between that animal and a cow, the attributes they have in common would, in some cases, be alone attended to, and in others form the chief object of consideration. In this manner, arbitrarily, or rather from the necessity of the case, we constantly direct our inquiries to abstract ideas, (which are more or less defective, when generally considered) instead of attending to the individuals as we must always do in the sensations; that is to say, when we observe and make experiments. And from these obvions truths we may see how it is that we acquire notions of genera, species, and individuals; how the first elements of language are formed by abstraction; how difficult it is to reason from sensations or experiments, by the use of ideas, which are their, necessarily imperfect, representatives; and how easy it is for us to mislead ourselves, and others, by paralogism, in the use of general propositions, if we do not constantly adhere to the same degrees of abstraction, or if we do not, in all practical applications, again introduce the abstracted parts, which, though we may have rejected them (like numbers in algebra) for the facility of our mental process, must invariably be resumed whenever the theatre of nature or society is, to be again entered.

These are the principal outlines of the science which treats of ideas, or the materials of our knowledge, and the conduct of mind, in the disposition and treatment of them. Most writers have treated this sub