exposure is effected in the parts themselves by means of the air-vessels, which ramify most minutely over the whole body. "En un mot, le sang ne pouvant aller chercher l'air, c'est l'air, qui va chercher le sang."

The heart of the crustacea, according to Cuvier, has no auricle; and it is what he calls an aortic heart. For it expels the blood into the arteries of the body; and this fluid passes through the gills previously to reaching the heart again. The different parts of the system are here found under a mode of connection exactly the reverse of what we observe in fishes, where the blood is sent into the gills, and passes subsequently into the aorta. The circulating organ in that class is therefore a pulmonary heart.

According to Cuvier, the cuttle-fish has three hearts, neither of which pos sesses an auricle. Two of these organs are placed at the root of the two branchia: they receive the blood from the body, (the vena cava dividing into two branches, one for each lateral heart,) and propel it into the branchiæ. The returning veins open into the middle heart; from which the aorta proceeds.

The other mollusca have a simple heart, consisting of one auricle and ventricle. The vena cava assumes the office

of an artery, and carries the returning blood to the gills; whence it passes to the auricle; and is subsequently expelled into the aorta. Here therefore, as in the crustacea, the heart is a pulmo

nary one.

The vermes of Cuvier have circulating vessels, in which contraction and dilatation are perceptible, without any heart. They can be seen very plainly in the lumbricus marinus. The leech, naias, nereis, aphrodite, &c. are further examples of the same structure. This anatomist is of opinion that the mollusca, crustacea, and vermes, possess no absorbing vessels; and he thinks that the veins absorb, as he finds them to have communication with the general cavity of the body, particularly in the cuttle-fish. Hence the above mentioned classes will hold an intermediate rank between the vertebral animals, which possess both blood-vessels and absorbents, and the insects, which have neither.

ABSORBING SYSTEM.

The chyle of birds is transparent: and there are no mesenteric glands in these animals.

The lacteals are uncommonly numer

ous on the intestines and mesentery of the turtle, in which animal there are no absorbent glands.

The lymphatics of fishes have neither glands nor valves.

ORGANS OF RESPIRATION.

The incessant continuation of the great chemical process, by which oxygen is exchanged for hydrogen and carbon, is essentially necessary to the well being of the greater part of animals. Yet the organs and mechanism, by which this wonderful function is carried on, vary very considerably. In the mammalia, after birth; in birds, when they have left the egg; and in amphibia, when completely formed; the chief organ of this function is the lungs in fish it is performed in the gills; in most insects in their trachea; in the vermes, in analogous, but at the same time very different parts.

The respiratory organs of birds constitute one of the most singular structures in the animal economy, on account of several peculiarities which they possess ; but more particularly in consequence of their connection with the numerous aircells, which are expanded over the whole body.

The lungs themselves are comparatively small, flattened, and adhering above to the chest, where they seem to be placed in the intervals of the ribs; they are only covered by the pleura on their under surface, so that they are in fact on the outside of the cavity of the chest, if we consider that cavity as being defined by the pleura: a great part of the thorax, as well as the abdomen, is occupied by the membranous air-cells, into which the lungs open by considerable apertures. Those of the thorax are divided, at least in the larger birds, by membranous transverse septa, into smaller portions; each of which, as well as the abdominal cells, has a particular opening of communica tion with the air-cells of the lungs, and consequently with the trachea. The membranes of these cells, in the larger birds, are provided here and there with considerable fasciculi of muscular fibres, which have been regarded as a substitute for the diaphragm, which is wanting in this class of animals. They also serve very principally, as we may ascertain by examining large birds in a living state, to drive back again into the lungs the air which they receive in inspiration; whence the repletion and depletion of the thoracic cells must alternate with those of the abdominal cavities.

Bsides these cells, a considerable portion of the skeleton is formed into receptacles for air in most birds, (for there are indeed exceptions and considerable variations in the different genera and species.) This structure is particularly marked in the larger cylindrical bones, as the scapula, clavicle, and femur. It is also found in most of the broad and multangular bones of the trunk, as the sternum, ossa innominata, dorsal vertebræ, &c. All these are destitute of marrow in the adult bird, at least in their middle; so that the cylindrical bones form large tubes, which are only interrupted towards the extremities by a sort of transverse bony fibres: the broad bones are filled with a reticulated bony texture, the cells of which are empty. They have considerable apertures, (most easily shewn in those extremities of the cylin. drical bones which are turned towards the sternum) communicating with the lungs by small air-cells; which facts may be shewn by various experiments on living and dead birds.

These receptacles of air probably serve the purpose of lightening the body of the bird in order to facilitate its motions. This effect is produced in most birds to assist their flight; in some aquatic species for the purpose of swimming; in the ostrich, and some others, for running. Hence we find the largest and most numerous bony cells in birds which have the highest and most rapid flight, as the eagle, &c. And hence also the bones of the bird which has just left the egg are filled with a bloody marrow, which is absorbed soon after birth, entirely in some, in others, particularly among the aquatic species, at least for the greater part.

Besides the uses which have been already pointed out, these receptacles of air diminish the necessity of breathing frequently, in the rapid and long continued motions of several birds, and in the great vocal exertions of the singing

birds.

The lungs of amphibia are distinguished from those of warm-blooded animals, both by a great superiority in point of size, as well as by a greater looseness of texture, arising from the great size of their air-vessels. In frogs, lizards, and serpents, the lungs consist of a cavity, whose sides are cellular. The posterior part of the organ either forms a mere membranous bag, or else the cells are larger there than elsewhere. In the turtle the vesicles are very

large, but the texture is uniform through.

out.

In the tadpole, and the young of such lizards as bring forth in water, there are two organs, which somewhat resemble the gills of a fish (appendices fimbriata, Swammerdam.) These serve for the purposes of respiration while the animal lives in the water. They are connected to the sides of the neck, and hang loose from the animal; they are not permanent, but are gradually withdrawn into the chest, (within a few days, in the reptiles of this country,) where their remains may still be perceived for some time near to the true lungs. Instead of the branchial opening, by which fishes again discharge the water which they have taken in at the mouth, some, tadpoles have for this purpose a canal on the left side of the head, near the eye; which must be distinguished from the small tube on the lower lip, by which they attach themselves to aquatic plants.

Instead of lungs, fishes are furnished with gills or branchiæ; which are placed behind the head, on both sides, and have a moveable gill cover (operculum bran chiale,) which is wanting in the order of pisces chondropterygii only. By means of these organs, which are connected with the throat, the animal receives its oxyen from the air contained in the wa ter; as those animals which breathe de rive it immediately from the atmosphere. They afterwards discharge the water through the branchial openings (apertu ræ branchiales;) and therefore they are distinguished from animals of the three preceding classes by this circumstance; viz. that they do not respire by the same way that they inspire.

We have already shewn, in speaking of the organs of circulation, how the gills receive the venous blood by means of the branchial artery, and how this blood is sent into the aorta after its conversion into the arterial state. The distribution of these vessels on the folds and divisions of the gills constitutes one of the most delicate and minute pieces of structure in the animal economy.

Each of the gills consists in most fishes of four divisions, resting on the same number of arched portions of bone or cartilage, connected to the os hyoides. Generally there is only a single opening for the discharge of the water; but in many cases, particularly among the cartilaginous fishes, there are

several.

Many animals of this order possess a single or double swimming bladder; which has been found in different in stances to contain azote, hydrogen, and oxygen. It has not been hitherto determined, whether it be subservient to any other functions, besides that well known one from which its name is derived. In the mean time, like the air receptacles of birds, it may be considered, without impropriety, in the present division of the work.

It is placed in the abdomen, and closely attached to the spine. It communicates generally with the esophagus, and sometimes with the stomach, by a canal (ductus pneumaticus,) containing in some instances, as the carp, valves which seem to allow the passage of air from the bladder, but not to admit its entrance from without.

That white-blooded animals indispensably require a species of respiration would have been inferred, by analogy, from the wonderful apparatus of gills or trachea, which have been discovered in most orders of both classes of these beings. But in many cases direct proof has been obtained on this point: experiment has actually proved the exchange of carbon for

oxygen.

White-blooded animals are moreover distinguished from those which have red blood by this circumstance: that none of the former, as far as we hitherto know, take in air through the mouth.

Many aquatic insects, as the genus can. cer, have a species of gills near the attachment of their legs. The others, and par ticularly the land-insects, which constitute, as is well known, by far the greatest number of this class of animals, are furnished with air-vessels, or trachea, which ramify over most of their body. These trachea are much larger and more nume. rous in the larva state of such insects as undergo a metamorphosis, (in which state also the process of nutrition is carried on to the greatest extent) than after the last, or, as it is called, the perfect change has taken place.

A large air-tube (trachea) lies under the skin on each side of the body of larvæ, and opens externally by nine apertures (stigmata): it produces on the inside the same number of trunks of airvessels (branchia.) which are distributed over the body in innumerable ramifi

cations.

Both the trachea and branchia are of a shining silvery colour; and their principal membrane consists of spiral fibres. The most numerous and minute ramifi

cations are distributed on the alimentary canal.

There is great variety in the number and situation of the external openings, by which insects receive their air.

In most instances the stigmata are placed on both sides of the body. The atmospheric air enters by an opening at the end of the abdomen in several aquatic larvæ, and even perfect insects. A very remarkable change in this respect takes place in several animals of this class during their metamorphosis. Thus in the larva of the common knats (culex pi piens,) the air enters by an opening on the abdomen while in the nympha of the same animal it gains admission by two apertures on the head.

In the class of vermes, which comprehends such very different animals, the structure of the respiratory organs is proportionally various. Some orders, as those which inhabit corals, the proper zoophytes, and perhaps the intestinal worms, appear to be entirely destitute of these organs: so that if any vital function, analogous to respiration, is carried on in these animals, it must be effected by methods which yet remain to be discovered.

In

Those vermes, however, which are furnished with proper organs of respira tion, have the same variety in their structure which was remarked in insects. Some, as the cuttle-fish, oyster, &c. have a species of gills, varying in structure in different instances. But the greatest number have air-vessels, or tracheæ. Several of the testaceous vermes have both kinds of respiratory organs. some of the inhabitants of bivalve shells, as the genus venus, the air-vessels lie between the membranes of a simple or double tubular canal, found at the anterior part of the animal, and capable of voluntary extension and retraction. It serves also for other purposes, as laying the eggs. The margins of its mouth are beset with the openings of the trachea.

In the terrestrial gasteropodous inof lusca, of which we may infance the snail and slug, there is a cavity in thes neck receiving air by a small aperture, which can be opened or shut at the of the animal. The pulmonary vessels ramify on the sides of the cavity,

ORGAN OF THE VOICE.

Aristotle has correctly observed, that those animals only which possess lungs, consequently the three first classes of the

animal kingdom, possess a true voice. Several genera and specics even of these are either entirely dumb, as the anteater, the manis, the cetacea, the genus testudo, several lizards, and serpents; or they lose their voice in certain parts of the earth, as the dog in some countries of America, and quails and frogs in several parts of Siberia.

Most mammalia have the following circumstances in common: their rima glottidis is provided with an epiglottis, which in most instances has a peculiar muscle, arising from the os hyoides, and not found in the human subject: the mar gins of this rima are formed by the double ligamenta glottidis (ligamenta thyreoarytanoidea); between which the ventriculi laryngis are formed. The epiglottis does not exist in most of the bat kind: and in some mouse-like animals, as the rell-mouse (glis esculentus,) it is hardly discernible. The superior ligamenta glottidis, as well as the ventriculi laryngis, are wanting in some bisulca, as the ox and sheep.

Some species of mammalia have a peculiar and characteristic voice; or at least certain tones, which are formed by additional organs. Of this kind are cer tain tense membranes in some animals; and in others peculiar cavities, opening into the larynx, and sometimes appearing as continuations of the ventriculi laryngis.

The neighing of the horse, for example, is effected by a delicate and nearly falciform membrane, which is attached by its middle to the thyroid cartilage, and has its extremities running along the external margins of the rima glottidis.

The peculiar sound uttered by the ass is produced by means of a similar membrane, under which there is an excavation in the thyroid cartilage. There are moreover two large membranous sacs openng into the larynx.

The mule does not neigh like the mare by which it was conceived, but brays like the ass which begot it. It possesses exactly the same larynx as the latter, without any of the peculiar vocal organs of the mother; a fact which, like many others, cannot be at all reconciled with the supposed pre-existence of previous ly formed germs in the ovarium of the mother,

Several apes and baboons, as also the rein-deer, have on the front of the neck large single or double laryngeal sacs, of various forms and divisions, communicating with the larynx by one or two open

ings between the os hyoides and thyroid cartilage.

Some of the cercopitheci, as the C. Seniculos, and beelzebub, have the middle and anterior part of the os hyoides formed into a spherical bony cavity, by which the animals are enabled to produce those terrific and,penetrating tones, which can be heard at vast distances, and have gained them the name of the bowl. ing apes.

The most striking peculiarity in the vocal organs of birds, and which belongs to all birds, with very few excep tions, consists in their possessing what is commonly called a double, larynx, but which might be more properly described as a larynx divided into two parts, placed at the upper and lower ends of the trachea. They have also two rimæ glottidis.

The superior, or proper rima glottidis, is placed at the upper end of the tra chea; but is not furnished with an epi glottis. The apparent want of this organ is compensated in several cases by the conical papille placed at both sides of the

rima.

The apparatus which is chiefly concerned in forming the voice of birds is found in the inferior or bronchial larynx. This contains a second rima glottidis, formed by tense membranes, which may be compared in several cases, particular ly among the aquatic birds, to the reed at the mouth of musical instruments. It is furnished externally with certain pairs of muscles, varying in number in the diffe rent orders and genera; and with a kind of thyroid gland. The course and pro portionate length of the trachea, and particularly the structure of the inferior larynx, vary very considerably in the different species, and even in the two sexes, especially among the aquatic birds. Thus, for example, the tame or dumb swan (anas olor) has a straight trachea; whilst in the male of the wild, or whist ling swan (cygnus), this tube makes a large convolution, which is contained in the hollow of the sternum. In the spoonbill (Platalea leucorodia), as also in the Phasianus motmot, and others, similar windings of the trachea are found, not enclosed in the sternum. The males of the two genera, anas and mergus, have at their inferior or bronchial larynx a bony cavity, which contributes to strengthen their voice.

A very little comparison of the me chanism of wind musical instruments with the organs of the voice in birds, will show how nearly they are allied to each

other; and it may be observed, that the sound produced by some of the larger birds is exactly similar to the notes that proceed from a clarionet or hautboy in the hands of an untutored musician. The inferior glottis exactly corresponds to the reed, and produces the tone or simple sound. The superior larynx gives it ut terance, as the holes of the instrument; but the strength and body of the note depend upon the extent and capacity of the trachea, and the hardness and elasticity of its parts. The convolution and bony cells of the windpipe, therefore, may be com. pared with the turns of a French horn, and the divisions of a bassoon; and they produce the proper effects of these parts in the voices of those birds in which they are found.

BRAIN AND NERVES, AND ORGANS OF

SENSE.

The parts subservient to the animal functions, which, constituting the leading character of animals, have derived their name from that circumstance, afford to our observation a more clear and manifest gradation, from the most simple to the most compound structure, than any others in the animal economy.

In some of the most simple animals of the class vermes, particularly among what are called zoophytes, little or no distinction of similar parts (or structures) can be discerned, and we are unable to recognize any thing as a particular ner. vous system, or even as a part of such a system. The power of sensation and voluntary motion which these possess, as well as any other order or class of the ani mal kingdom, proves that the nervous matter must be uniformly spread throughout their homogeneous substance. The almost transparent polypes (hydra,) which are often found with a body of an inch in length, and arms or tentacula of a proportionate size, appear to consist, when surveyed in the best light by the strongest magnifying powers, of nothing but a granular structure connected into a definite form by a gelatinous sub

stance.

In many other vermes, and in insects, particular nerves can be distinguished, arising in general from a chord running the whole length of the body, and called the spinal marrow, the superior extremity of which part, slightly enlarged, constitutes the brain. The latter organ, however, in both classes of cold and redVOL. III.

blooded animals, and still more in those which have warm blood, has a much more complicated structure, and a far greater relative magnitude: all animals are, however, exceeded in both these points by the human subject, which, according to the ingenious observation of the learned Sömmerring, possesses by far the largest brain, in proportion to the size of the nerves which arise from it.

The vast superiority of man over all other animals in the faculties of the mind, which may be truly considered as a general distinction of the human subject, led physiologists, at a very early period, to seek for some corresponding difference in the brains of man and animals. They naturally investigated the subject, in the first instance, by comparing the proportion which the mass of the brain bears to the whole body; and the result of this comparison in the more common and domestic animals was so satisfactory, that they prosecuted the inquiry no farther, but laid down the general proposition, which has been universally received since the time of Aristotle, that man has the largest brain in proportion to his body. Some more modern physiologists, however, in following up this comparative view in a greater number of animals, discovered several exceptions to the general position. They found that the proportion of the brain to the body, in some birds, exceeds that of man; and that several mammalia (some quadrumana, and some animals of the mouse kind) equal the human subject in this respect.

As these latter observations entirely overturned the conclusion which had been before generally admitted, Sömmerring has furnished us with another point of comparison, that has hitherto held good in every instance: viz. that of the ratio, which the mass of the brain bears to the nerves arising from it.

Let us divide the brain into two parts; that which is immediaely connected with the sensorial extremities of the nerves, which receives their impressions, and is therefore devoted to the purposes of animal existence. The second division will include the rest of the brain, which may be considered as connecting the functions of the nerves with the facul ties of the mind. In proportion then as any animal possesses a larger share of the latter and more noble part; that is, in proportion as the organ of reflection exceeds that of the external senses, may we expect to find the powers of the S s