Fel. Order IV.-Malacopterygii Apoda. Order VI.-Plectognathi. This order, the last of the osseous Fishes, approaches the cartilaginous in many points of its organization; principally, however, in the slow ossification of the skeleton, and the imperfect structure of the mouth. They derive their name, as already stated, from the union of the upper jaw to the skull; so that its motion is obtained, not from a distinct joint, but by the mere flexibility of the half-ossified cartilages. The gill-lid is concealed under the thick skin, with only a small opening; the ribs are scarcely developed; and there are no true ven The fishes in which the ventral fins are wanting form tral fins. This order contains two families. but one natural family, the MURENIDE, or El tribe. They are all lengthened in form, have the spine extremely flexible, the skin thick and soft, and the scales almost invisible. In most of them the external gill-apertures are very small, and open very far back; by which arrangement they are enabled to keep the gills moist for a long time when out of water, whilst the roundness and flexibility of their bodies facilitate their motion upon land. Many of them inhabit rivers, whilst others are exclusively marine. The eel is the kind most abundant in Britain. The conger is a marine eel, frequenting the European seas; it is one of the largest of the family, being from four to six feet long, and as thick as a man's leg. The gymnotus, or electric eel, Gymnotus. is a native of the South American rivers. It attains the length of five or six feet, and communicates shocks so powerful that men and horses have been stunned by them. This power seems voluntary, and can be sent in a particular direction, or even through the water, the fish in which are killed or stunned by its shocks. By giving these it is greatly exhausted, and requires rest and nou rishment before it can renew them. Order V.-Lophobranchii. This order is a very small one, containing but one family, of which the genera are few. Their appearance is very peculiar. The tufted gills are covered by a large operculum; but this is bound down by membranes on all sides, so that there is only one small hole for the water to escape. The body is covered, not with small scales, but with shields or plates, which often give it an angular form. In general they are of small size, and almost without flesh. The syngnathus possesses a long tubular snout; it is peculiar for, the protection which it affords to its young, which resembles that provided in the marsupial Mammalia. The eggs are conveyed into a sort of pouch under the body of the male, and are hatched there, the young fry afterwards finding their way out. Some of these are found in the British seas, as are also the hippocampi, commonly called sea-horses, from the resemblance, of the upper part of the body (especially when the dead specimen bends in drying) to the head and neck of a horse in miniature. Their tail is prehensile, and they climb or hold on to the stalks of marine plants, by its means. Some of this family are almost destitute of fins, having none but the dorsal. Diodon. 1. The GYMNODONTES, or Naked-Toothed Fishes, are distinguished by having the jaws covered with a substance resembling ivory, arranged in small plates (which are reproduced as soon as destroyed by use), and really representing united teeth. They live on crustacea and sea-weed, and their flesh is not palatable. Some species are reputed to be poisonous, at least at particular seasons. The most remarkable species of this family are the spinous globe-fishes, diodon and tetraodon (their technical names being derived from the apparent division of their jaws into two and four tooth-like pieces respectively), which have the power of blowing themselves up like balloons, by filling with air a large sac which nearly surrounds the abdomen. When thus inflated, they roll over with the belly upwards, and lose all power of directing their course; but they are remarkably defended by spines over their whole surface, which are erected as they are inflated. They are mostly inhabitants of warm seas, but a specimen is occasionally drifted to our coast. The sun-fish has a body of somewhat similar form, but incapable of inflation; the tail is so short that it looks like the anterior half of a fish cut in two in the middle. Some species attain an immense size. One which is occasionally taken on the British coast has been known to weigh 300 lbs., and others are much larger. DIVISION II. CHONDROPTERYGII OR CARTILAGINOUS the opening of the jaws in the largest individuals is sufficient to admit with ease the body of a man. The mouth is placed on the under surface of the head, from FISHES. The skeleton of these fishes is not entirely devoid of calcareous matter, but this is disposed in separate grains, and does not form fibres or plates. Hence the hardest portions of the framework remain quite flexible. The freedom of motion of the spinal column, which is characteristic of fishes in general, is here still further increased, in many species at least, by the continuation of the sac containing gelatinous matter (which in the osseous fishes was simply interposed between each pair of vertebræ) through the whole column, the bodies of the vertebræ being pierced in the centre so as to form a continuous tube. This division contains two subordinate groups: in the first, the gills are attached by one edge only, hanging in fringes as in the osseous fishes; in the second, they are so attached to the skin by the second edges, that the water cannot escape from their intervals except by holes in the surface. Accordingly, instead of having a single pair of large apertures, with a valvelike cover, or operculum, behind the head, they have as many apertures on each side as there are arches of gills. The first series contains but one order, and the second the other two. Order VII.-Chondropterygii Branchus Liberi. This order contains only one family, the STURIONES, or Sturgeon tribe. In many of its characters, as well as in the disposition of the gills, it is intermediate between the Osseous Fishes and the Shark tribe, which may be regarded as the types of the Cartilaginous division. Sturgeons are chiefly river fish, and from their large size, vast numbers, and the quantity of food and other important products they afford, are extremely valuable to man. The common sturgeon of the British shores is about six feet long, and its flesh is somewhat like veal. The rivers falling into the Black and Caspian Seas, however, produce several other species, of which the largest not unfrequently attains the length of fifteen feet, one individual being recorded as having weighed 3000 lbs. The roe of the sturgeon furnishes the caviar so much esteemed in Russia; and its air-bladder furnishes isinglass. The section of CHONDROPTERYGII BRANCHIIS FIXIS is divided into two orders, the first having teeth, and the second having the mouth formed into a sucker. Order VIII-Selachii. This order only comprises one family, that of Sharks and Rays. A great metamorphosis here takes place in the condition of the bones of the mouth, those which are commonly termed the jaws, in which the teeth are fixed, being very different in position and character in osseous fishes, and the true jawbones not being here developed. This tribe is distinguished from other fishes by many peculiarities: in several members of it the young are produced alive, the eggs being hatched within the body of the parent; and in others the eggs are enclosed in a peculiar horny casing, which has often long tendril-like appendages, that coil round and attach them to other bodies. This is the case with the eggs of the common dog-fish of our coast, vulgarly known as sea-purses. The Sharks much resemble ordinary fishes in their form, having the gill-openings on the sides of the neck, and the eyes on the sides of the head, in both of which respects the Rays differ from them. The dog-fish of the British coasts differs but slightly from the true sharks, and is, in its way, equally voracious. The white shark is the most celebrated species of the tribe, being, from its size and voracity, the terror of mariners in the seas it inhabits. It frequents warm latitudes, but has occasionally visited the British shores. It has been known to attain a length of thirty feet, and, of the head at each side in the form of a double-headed hammer, with an eye in the middle of each extremity. The pristis, or saw-fish, is another interesting genus. Its general form and character is like that of the sharks, but the snout is extended like the blade of a sword, with strong and cutting tooth-like spines on both edges. With this formidable weapon the fish, which sometimes attains the length of from twelve to fifteen feet, will attack the largest whales, and inflict dreadful wounds. To the shark tribe also belongs the angel fish of our own coasts, which forms the link to the rays in its general structure and aspect. The eyes are situated on the back or upper surface of the head; the body is broad and flattened horizontally, and the pectoral fins widely expanded. It commonly grows to the length of seven or eight feet; its appearance much belies its name, being (according to our ideas of beauty) one of the ugliest of fishes, but its flesh is by no means unpalatable. The Rays are less numerous than the Sharks, and abound rather in temperate than in tropical seas. They are characterized by the extreme horizontal flattening of the body, in which, however, there is not (as in the Pleuronectidae) any want of lateral symmetry. The two sides are expanded horizontally, and unite with the expanded and fleshy pectoral fins to form one continu-| altogether of lower organization than the lamprey; but sus surface. The eyes are placed on the back or upper the species that differs most in its general characters surface, whilst the mouth, nostrils, and gill-openings, from the rest of the class is the amphioxus, or lancelot. are below. To this group belong the rays and skates, This is a very small animal, about an inch long, somethornbacks, and other species; but the most interesting times found lurking under stones in pools left by the of all is the torpedo, or electric ray, sometimes found on ebbing tide. It is destitute of almost every one of the the Channel coast of England, but more abundant in characters which have been mentioned as peculiar to vertebrated animals; and, nevertheless, can scarcely be classed anywhere else than with this family. Torpedo. the Mediterranean. The electric apparatus is of very similar structure with that of the gymnotus, and it is disposed in the space between the pectorals and the head and gills. The shocks given by this fish, though smart, are not so benumbing as those of the gymnotus; their use in its economy are not apparent, as the animal can obtain its prey without them. The flesh of the rays is wholesome, and that of most species agreeable as food. The skin of some of them is employed in the arts for polishing, and, from that of others, shagreen is made. Order IX-Cyclostomata. The third order of the Cartilaginous Fishes, and the last of the class, is one which contains comparatively few species, and these exhibiting but a very low degree of organization. They take their name from the adaptation of the mouth to the purposes of suction, by its transformation into a round fleshy disk, having the oral opening in the centre, and the margin supported by a ring composed of the cartilaginous jaws united together. The spinal column loses its distinct division into vertebræ, the space elsewhere occupied by their bodies being traversed from end to end by a cylindrical membranous tube filled with a mucilaginous fluid; and this, in the higher species, presents cartilaginous rings at intervals, which are the rudiments of vertebræ; whilst, in the lower, there is no vestige of these bodies, and the whole structure is reduced to the level of that of the Annelida. The pectoral as well as the ventral fins are absent; and the skin is soft and mucous, with scarcely a vestige of scales. This order contains but a single family. The lampreys are the most allied to other fishes in their general organization; they possess teeth within the ring, and Lamprey. with these they tear the bodies of the animals to which they attach themselves. There is a marine species two or three feet long, and other smaller ones which inhabit rivers. The myxine or hag is destitute of eyes, and is SUB-KINGDOM-ARTICULATA. From the Vertebrata, we might pass, in descending the animal cale, either to the Mollusca, or the Articulata, both of which exhibit some points of approximation with them. In both we meet, as in the Vertebrata, with very highly organized, as well as very simply constructed beings. In both we find animals much superior to the lowest Vertebrata; and in both, also, we find species which are in many respects below the highest Radiata. It is the necessary consequence of a natural arrangement, which aims at grouping together the different forms of living beings according to the type or plan on which they are constructed, that such should be the case. Neither of these two sub-kingdoms can be regarded as in all respects superior to the other. The high development of the locomotive power in the Articulata strikingly contrasts with its usually slight possession by the Mollusca. On the other hand, the digestive and nutritive systems in the Mollusca are much more complex, and attain a higher organization; so that the heart, for example, of the Tunicata is as powerful in its action on the circulating fluid as that of the highest Articulata. the whole, however, the Articulata should be regarded as ranking above the Mollusca in the animal scale, since it is in the animal powers that the former have the superiority. On The general character of the series has been already stated as being the jointed or articulated character of the skeleton or hard portion of the structure, and the enclosure of the whole body in this. Nothing can be found in the Mollusca at all approaching in character to the shell of a lobster or the horny case of the beetle. It is the peculiarity of the skeleton in the Articulata, that it not merely encloses the body, but is prolonged over the appendages for locomotion, where they exist; and he portions of it which cover these are also jointed, for the sake of conferring upon them the requisite flexiblity. This structure is more apparent, however, in some cases than in others. In the lowest animals of this series, where there are no appendages for locomotion, and where all movements are effected by the body itself, this is endowed with great flexibility, and the whole envelope is so soft that the division into segments can scarcely be recognised. This is the case, for example, in the leech and earthworm. The articulated character is most apparent in the Centipede tribe, where the segments are all of nearly equal size, and where each possesses a short pair of legs, which are themselves also articulated. But in the highest classes of this sub-kingdom we again lose the appearance of the division into segments, from an opposite cause-the consolidation of several rings into one piece. In proportion as the locomotive power is more intrusted to the extremities, so does it become unnecessary that the trunk should possess much flexibility; and in the same proportion does it become necessary that the portion of it from which arise the muscles of those extremities should be very firmly framed. Accordingly, the part of the body behind the head, which is called the thorax, and from which the legs and wings of Insects, and the principal walking legs of Crustacea have their origin, very commonly appears as if composed of ore piece, although it is really made up of three or mor segments, each one of which gives origin to a pair of members. The Articulata are almost invariably of small size; and the bulk of their bodies is made up, not by their digestive and nutritive apparatus, but by the muscles which move it. It is only in those which approach the Mollusca in the vegetative nature of their existence, that we find any considerable dimensions attained. As the Mollusca are an essentially aquatic group, so are the Articulata principally adapted to atmospheric respiration; and the most active among them can even quit the surface of the ground and mount up into the air. We find their respiratory apparatus constructed, therefore, upon an opposite plan. Instead of the blood being sent into external prolongations of the surface-the gills to meet the air contained in the surrounding fluid, the air is introduced into the body to meet the blood, this being distributed on the sides of cavities or tubes into which it enters. In Insects these tubes have a very complex and beautiful distribution through the Dody. The Articulata exhibit a peculiarity in the nervous system, which often enables the real character of doubtful animals to be distinguished. A double cord runs along the centre of the lower surface of the animal, studded with knots or ganglia at regular intervals, which are so many centres from which the nerves pass off to the different segments. The head, also, has its ganglia, in which the double cord terminates anteriorly. Where the members, however, are not uniformly distributed along the whole body, but are concentrated to one part, as in Insects, Arachnida, and the higher Crustacea, we observe a corresponding concentration of the ganglia in that region. The degree of this concentration indicates the elevation of the animal in the series. The following classes must be arranged in the articulated series, though in some of them the characteristic structure is very indistinct : ANNELIDA, or Worm tribe. In these the body is prolonged, without any distinct appendages for locomotion. The habitation is usually aquatic, though sometimes terrestrial. The division into segments is not very distinct, the entire skin being soft. MYRIAPODA, or Centipede tribe. These have also a prolonged body, but it is provided with legs; and the articulation of the covering both of the body and legs is very distinct. INSECTS, which are distinguished in their perfect state by the possession of one or two pairs of wings; by the restriction of the legs, which are never more than six in number, to the thorax; and by the division of the trunk into three portions, the head, thorax, and abdomen, which are usually very distinct from one another. They are also distinguished by their remarkable metamorphosis, commencing from a form which resembles that of the Annelida. ARACHNIDA, the Spider and Scorpion 'tribe, which differ from insects in having the head and thorax united, in undergoing no metamorphosis, and in having eight or more legs. CRUSTACEA, which have a hard envelope, principally composed of earthy matter, and which are adapted for aquatic respiration. Many of them have the form of insects; but their legs are never less than ten in number. I'he foregoing constitute a tolerably regular series, into which we must also introduce the ENTOZOA, which seem to exhibit the characters of the Worm tribe in their most degraded condition, and the animals composing which are parasitic upon or within others; the ROTIFERA, or Wheel-Animalculæ tribe, of which some approach the Polypifera and Polygastrica, while others approximate the Crustacea; and the CIRRHOPODA, or Barnacle tribe, which bear a strong general resemblance to the Mollusca, put unquestionably belong to this series. CLASS VI-INSECTS. The class of Insects is perhaps the most interesting in the whole animal kingdom, both in regard to the num ber, variety, beauty, and complexity, of the different forms which it contains, the vast assemblages of individuals of the same species which not unfrequently make their appearance together, and their consequent import ance in the economy of nature. The true INSECTS are distinguished from the Crustacea by their peculiar apparatus for atmospheric respiration; from the Arachnida by having but six legs (eight being the number in that class), and by the division of the body into three parts; and from the Myriapoda by the limited number of legs and segments, the latter seldom exceeding thirteen. In the perfect Insect it is sometimes difficult to distinguish the division into segments: they may generally be seen, however, on the lower side of the body, especially on the abdomen. But in the larva or caterpillar state they are never obscure, and their number is very constant, being almost always thirteen, one forming the head. Of the twelve segments of the body, three in the perfect insect form the thorax, or division succeeding the head, while the remaining nine constitute the abdomen. It is more common for one or two segments to be apparently deficient (being consolidated with the rest), than for any increased number to be present. The metamorphosis, or complete change of form, which may be seen in the greater number of insects during their development, has attracted much attention from the earliest ages to the present time. The larva, which afterwards changes to a beetle, a butterfly, or a wasp, bears no resemblance whatever to the perfect or imago form and is in fact allied, in almost every particular of its conformation, to a class far beneath. Moreover, it has to go through an intermediate form-if any thing still more remarkable-that of the pupa or chrysalis, in which there is an almost complete cessation of activity, but in which preparation is being made for the exit of the perfect insect at its final change. The alteration of the entire character of the animal is no less remarkable then its change of form. In the larva condition, its whole energies seem to be concentrated upon the nutritive functions; the voracity is extreme, and the increase in the weight of the body is very rapid; while, in the perfect insect, the body undergoes little increase of size, but it is provided with powers of active movement, and these are principally destined to enable it to seek its mate, for the purpose of propagating its race. The larva, when it first emerges from the egg, bears but a very small proportion to its subsequent bulk. According to Lyonnet, the comparative weight of a fullgrown caterpillar of the goat-moth to that of the young one just crept out of the egg, is as 72,000 to 1. During its increase, it throws off its skin several times, like the Crustacea. The larvæ in the different tribes vary extremely as to the degree of their development: in some orders they are extremely imperfect, not even possessing legs; while in others they correspond with the perfect insect in almost every particular except the presence of wings. After attaining its full growth in the larva condition (the bulk of the body in this state often much exceeding that of the imago), the insect undergoes a very remark able change, ceasing to take food, and apparently losing all appearance of vitality. In this state it is termed the pupa or chrysalis. Many larvæ enclose themselves in a ilken cocoon, or in some other kind of envelope, before undergoing this change; and remain in it during the whole period of inactivity, which is sometimes many months in duration. Others bury themselves in the ground; and others, again, suspend themselves in the air. The pupæ of different orders of insects vary, like the larva, both in form and in degree of torpor. Some have the whole body enclosed in a horny case, without vestige of members, and are totally inactive, except when disturbed; while others present the general form of the perfect insect, but appear as if the body and limbs were separately bandaged and laid in close apposition; while others retain all their limbs free, and suffer no diminution in their locomotive powers or in their appetite for food. These, indeed, can scarcely be said to pass into the pupa state at all, their condition being only indicated by the gradual development of the wings. This development is equally taking place beneath the envelope of the pupae that are enclosed and inactive. The perfect insect or imago, when it emerges from its pupa case, exhibits in all respects the form which is characteristic of the species, and, in general, the size also; few growing much after they have attained this condition, and many scarcely eating at all. As already mentioned, the twelve segments forming the body of the larva, may still be recognised here, but very much changed in their character. The three anterior ones are often soldered, as it were, together; forming but one strong sheath for that portion of the body from which the wings and legs proceed, and this sheath affords firm attachment for the powerful muscles which move these organs. Those which constitute the abdomen, however, retain much more of their original aspect. The head is now quite distinct from the body, and connected with it by a neck, which is often very narrow. From each of the segments of the thorax a pair of legs proceeds; and the second and third usually give origin to a pair of wings each. Where, however, only one pair of these organs exists, they proceed from the second segment. The segments of the abdomen never show any vestige of legs. The accompanying diagram represents the chief parts of the perfect insect; the three segments of the thorax are separated from each other to show the organs attached to them. Segments of Insects. The especial function of the perfect insect is the continuance of the species; and the wings enable it to seek its mate, and to obtain a situation fit for the deposition of its eggs, which are always laid in the neighbourhood of whatever substances will supply the larva with nourishment, although it most commonly happens that the imago does not feed upon them. Many insects, such as the silk-worm moth and the ephemera or May-fly, die soon after having fulfilled this object, to which they pro ceed very soon after their last change. morphosis is said to be complete; but if the larva is more advanced, and the pupa differs little from it and from the perfect insect, the metamorphosis is termed incomplete. Insects, in their perfect state, are distinguished beyond all other animals for their power of locomotion, and for the perfection of their instinctive actions. In estimating their power of locomotion, the space traversed is of course compared with the length of the body; and thus it is seen that, rapid as is the flight of many birds, that of most insects far surpasses it. The senses of insects appear to be acute. They have generally large eyes, formed, in fact, by the union of a great number of small ones often several thousand; and although these are fixed, yet, from their being directed at various angles to each other, a great range of vision is obtained. It is be lieved that insects possess the power of hearing, and also of smell; though no distinct organs for receiving such impressions have been satisfactorily determined. That they have a delicate sense of touch in some part of the body, even where the general envelope is firm, cannot be questioned; and, from observations made upon the social insects, such as bees and ants, there is reason to believe that they communicate with each other by this sense. However extraordinary is the metamorphosis of insects, it is by no means unique, as was formerly supposed. The change of the tadpole into a frog, is an exact parallel to it; for the tadpole is for the time a fish, resembling that class in its entire organization, just as the maggot is for the time a worm. Moreover, we shall hereafter see, in some of the lower classes, a change which is fully as reinarkable. When the larva is very imperfect, and the pupa inactive, so that its change to the form of the perfect insect is very striking, the metaVOL. II.-54 my m A mlp mp B The different organs on the head of insects, furnish, by their varieties of conformation, important characters in classification. It will, therefore, be necessary to describe these in some detail. The most important charac ters, upon which, in fact, the pri21 m mary subdivision of the class is founded, are drawn from the structure of the mouth; in one large group it is furnished with mandibles or jaws, adapted for biting and bruising; while in the other, it is provided with a haustellium or proboscis, adapted for suction. Hence the first group is termed MANDIBULATA, and the second HAUSTELLAta. These organs are, however, but different modifications of the same elements. mx 12'c2 m 21 m mx mp mp mx mx Of IP 12 €2 Different parts of the mouth of a beetle. In the mouth of the Mandibulata, six principal pieces may be readily distinguished. these, four are arranged in two pairs, which work against each other laterally; a fifth piece is above the upper pair, and a sixth below the lower. The two lateral pairs are the jaws; of which the upper pair is distinguished by the name of mandibles, and the lower by that of maxilla. The mandibles are usually the largest, and are very powerful organs; sometimes they are provided with sharp or toothed of scissors; and sometimes with hooked points, more edges, working against each other like those of a pair formidable, for the size of the animal, than the teeth of the tiger. These are the principal organs by which the food, of whatever description, is usually obtained; but in the bees and wasps, of which some species are adapted to obtain their nourishment by suction, they are the instruments by which their curious edifices are built up. In a word, as has been well remarked, they supply the place of trowels, spades, pick-axes, saws, scissors, and knives, as necessity may require. The maxillæ, or under pair of jaws, are of similar construction, but usually smaller and less powerful. The pieces which are applied above and below to the spaces left between the jaws, are termed lips; the upper one being particularized as the labrum, and the lower one as the labium. A, upper side; B, under side; C, parts separated: a a. antennæ; ee, eyes; 1 upper lip; mm, mandibles; m, maxilla; mp, maxillary palp'; 12, labium; p, labial palpi: c 2. chin or mentum. 2 N 2 |