CHAPTER II.
SUB-KINGDOM VII.—ARTICULATA.
This subdivision of the animal kingdom, containing articulated or jointed animals and insects, exceeds every other in the number and diversity of the species. The articulation may belong to their bodies, limbs, or outer covering. The tough shells of some, formed by a secretion of a hard, horn-like substance, have numerous segments, or rings, either closely joined and firmly cemented, as those about the head and thorax, or loosely cemented, as those which encompass the abdomen. The skeleton of some is external, and consists of these articulated segments, which serve the double purpose of framework and covering. The muscles, or elastic cartilages holding them together, are striated, or furnished with small grooves in the sheath or shell. If the animal has limbs, they also are jointed, and hollow.
Class I.—Crustacea, so called from the crust in which their soft bodies are encased. They are a very large family, mostly of air breathing animals, with enough in common to indicate their relationship, yet distinguished by a great diversity in their forms and modes of life. Some are very small, and are as numberless as the sands on the shore. Others, when their members are all extended, can stretch themselves over a circle several feet in diameter.
The chief orders of the Crustacea are the Barnacles,[1] the Water-flea, the Fourteen-footed Crustacea,[2] and Ten-footed Crustacea.[3]
The Crayfish may be taken as a type of the structure of the Crustacea. The body has two principal sections. The anterior, called the cephalo-thorax,[4] extends to the first distinctly marked ring, and the shield, thus far, is comparatively smooth, the segments fitting so closely as to be practically one. In front and between the two pairs of antennæ, or feelers, is a small pointed process in the place of the nasal organ, but serving some other purpose. At the base of each of the smaller antennæ, on the under side, is a minute sac, the mouth of which is protected with delicate hairs. These are the organs of hearing, and near them, on the outer side, are the organs of smell. The sense of touch is in the fine cilia that fringe the mouth and the antennæ.
There are numerous appendages. Of the five pairs of legs, the first two are provided with claws, or nippers. The fore-legs, or arms, have, in the place of hands, strong pincers, similar, but not entirely alike; the one with sharp edge and smaller teeth is used for cutting, the other for mashing, or grinding the food. The other legs terminate in feathery points, and are used, in part, for locomotion, and by the female for carrying her eggs. The posterior pair, called swimmerets, together with the expansion of the last segment of the abdomen into a kind of caudal fin, are the main dependence for swimming. The segments are so loosely jointed that the “tail” can be moved freely, and by flapping it the animal moves easily. As there is no neck, in order to see objects in different directions, the eyes are not sunk in the head, but placed at the extremities of little muscular processes, or “eye stalks,” which are movable, making even hind-sight practicable when backward motion is desired.
THE CRAYFISH.
The crayfish breathes through branchiæ, or gills, situated at the sides of the thorax, protected by the carapace,[5] or horny covering, under the edges of which the water and air reach the gills. Here a very curious appendage is attached, called the “gill bailer,” which moves back and forth, creating a current of water through the gills that finds its way out through an opening near the mouth.
Under the welded sheath or cover of the head are the mandibles, or jaws, between which the mouth opens; a short passage, leading to the capacious, gizzard-like stomach, is provided with grinders, to still further masticate the food before it passes into the intestine. The eggs are small, and attached by glutinous threads to the appendages until they are hatched; the young are also attached, until sufficiently developed to live apart from the parent.
This class of animals undergoes periodic changes which are attended with some degree of violence. The crustaceous covering is a kind of epidermis,[6] having beneath it the true skin. It is formed by some process of exudation from the growing body. This sheath, while soft, expands slowly, but when hardened, the growth is retarded, and in time it is found too small for convenience, so it is cast off, and a new and larger one supplied to take its place. In this process of moulting the animal attempts to put off its outer covering, not in fragments or parts, but in one piece, though many delicate attachments have to be sundered, membranes rent, and sometimes even a limb torn off in the resolute effort to undress. This can not be done at all times, or at any time, without special preparation. A period of apparent sickness precedes, and the muscular parts of the limbs become shrunken, so that they are more easily extricated. The loss of a leg is not so serious a matter, since the damage is repaired by a new one with the same form and articulations. As the work of repairing the limb begins at the joint nearest the body, if the member is torn between that and the extremity, the partially mutilated animal has the strange power of throwing off all that remains beyond that joint.
Of other crustaceans, the common lobster is in most respects so similar to that shown in the first diagram as to need no further description than to say the cephalo-thorax is comparatively smaller, while the forearms and claws are larger.
There are also marine crayfish that are very numerous about the coral reefs off the Florida coasts, and have substantially the same characteristics, only their claws are considerably less, and their ciliated antennæ larger.
Crabs are closely allied to lobsters, and belong to the highest orders of the crustaceans. The lengthened, loose-jointed abdomen of the typical crayfish is wanting, and there is a general concentration of the parts; all the most important viscera being included in the thorax, and covered by a single, closely compacted shield. There are many species of crabs, differing in other respects as well as in the form of the shell or back, which in some is nearly orbicular, in others it is oblong, longer than it is broad, or broader than it is long. They differ in the smoothness of their shells, and in the length of their legs, which they stretch out from under their horny covering. Their first pair of limbs is not fitted for locomotion, but shows a vigorous development of the strong claws and pincers of other decapod crustaceans. Though found in almost all seas, they are poor swimmers, their legs being formed for walking or creeping, rather than as oars to propel them through the water. They are found in pools, among seaweeds, and particularly in marshy places left by the receding tides. Most species live in water, some in moist places on land. Many kinds of crabs are used for food. Its black claws and broad carapace readily distinguish it from other species. From activity in seizing, tearing, and devouring their food, and from their pugnacity, crabs are interesting inmates of the aquarium. They also moult, or cast off their shells; not at regular seasons, but when the demand for more room requires it.
Class II.—Arachnida are closely related to the crustaceans, having, like them, the body divided into two sections—cephalo-thorax and abdomen. To the former are attached four pairs of legs, but the abdomen has no appendages for locomotion. There are about 5,000 species, produced from eggs, and undergoing no metamorphoses in their development.
The lowest forms, under the common name of Acarina,[7] have the anterior part in a mass with the abdomen, and short legs near the head, terminated in little claws suitable for taking hold of hairs and feathers. They are mostly parasitic, and all birds and animals, even parasites themselves, are liable to suffer from acarina peculiar to their own species. Pedipalpi[8] (scorpions), and Araneina[9] (spiders), though much larger, belong to this class. The body of the scorpion is divided into segments, though the anterior of the abdominal part seems but a continuance of the thorax, and is as large. It, however, soon tapers off into a long, jointed, tail-like process, in the terminus of which is its hooked sting, perforated and connected with the poison sac. In striking, the tail is raised over the back and struck down. Its other weapons are the crab-like claws on the strong forearms. The Araneina, at least some classes of them, are well known. The soft, unjointed body is separated from the thorax by a narrow constriction or tie, and at the posterior end there are little appendages called spinnerets, through which the silken lines issue that form the web. The hinder feet are skillfully employed in arranging the gossamer threads after patterns that are instinctively followed.
Class III.—Myriapoda, Centipedes,[10] have the thorax merged with the elongated abdomen, while the head is free. They resemble worms in form, but the skin is stiffened with chitine,[11] and the many legs are articulated. There are two orders: the Chilognatha,[12] which move slowly, and are harmless, the “thousand legged worm” is a representative, and the Chilopoda,[13] more active, and having a flattened body of about twenty segments, each carrying one pair of legs. Their mouths are armed with formidable fangs connected with poison glands. They are carnivorous, and may be distinguished by their general appearance, quicker movements, and by having longer antennæ than the innocent vegetarians.
THE HEAD OF AN INSECT.
Ex.—A, gula, or throat; b, ligula, or tongue; c mandibles; d, maxillæ, or inner jaws.
Class IV.—Insecta. The distinguishing characteristics of this class are that the head, thorax, and abdomen are distinct; that they possess three pairs of jointed legs, one pair of antennæ, and, generally, two pairs of wings. The skin is hardened, and to it the muscles are attached. The eyes are usually composed of a number of facets, from fifty in the ant to many thousands in the winged insects. As the eyes are not movable, these facets enable them to see in many directions.
The several parts of the head and its appendages are shown in our illustration. The sensitive palpi, or feelers, with the delicate hair-brush tips at the ends, may also be noticed. The mouth differs in different species, and is fitted for biting and masticating, or puncturing and sucking. The adaptation seems perfect. Of all animals belonging to the articulate type, the Insecta possess the highest instincts. To this class belong the following orders: I. Neuroptera,[14] or lace-winged insects, of which the Dragon-fly, or Devil’s Darning Needle, is a good representative. II. The Orthoptera[15] (straight-winged). They have four wings, the front pair thick and narrow, overlapping along the back; the hind pair broad, net-veined and folded upon the abdomen. The representative forms are Crickets, Grasshoppers, Locusts, and Cockroaches. III. Hemiptera[16] (half winged). To this order belong the wingless Bed-bug, the Squash-bug, the Seventeen-year Locust, and the Cochineal.
Coccus-cacti[17]. The Mexican cochineal insect is of great value as a dye, and from it the most beautiful scarlet and crimson colors are obtained. The female is wingless, and, as an uncomely parasite, lives and feeds on cactus plants, especially those of the nopal[18] species, native in Mexico and Peru. The male only is represented in the diagram, and magnified somewhat larger than life. They are comparatively few in number, and of no commercial value. The plants are cultivated for the purpose, and the care of the insects, which increase very rapidly, is an industry giving employment to thousands of laborers, and in some parts of Mexico the product of the cochineal farms is among the most valuable of their exports. Cortes[19] in the sixteenth century received instructions from the Spanish court to obtain cochineal in as large quantities as possible. The export became very large, both Spaniards and others becoming skilled in the use of the beautiful dye stuff, nearly a hundred years before its real nature was known. The dried insect being very small, and crushed in preparing it for market, it was supposed to be the seed of some plant; and it was not until in 1703 that its true nature was discovered by microscopic observations. The industry still flourishes in Mexico, but both plant and the insect have been taken to other countries, and do well. The annual export of cochineal from the Canary islands has, in the present century, amounted to over 6,000 tons, valued at more than $4,000,000. The manner of collecting the insects is very simple. When of sufficient age, some already dead, and others yet alive, they are brushed off into bags, and the living killed by holding them either in boiling water or heated ovens, and then exposed in the sun till quite dry. The dried insects have the form and appearance of irregular fluted and concave grains, of which it is estimated there are 70,000 in a pound.
THE COCHINEAL.
There are several species of these insects, alike in form and habits, but not alike useful. Some, as the Scale insect, are a great annoyance to gardeners, and destructive to our house plants. Others, as the Wax insect, live on certain tropical trees, and soon entomb themselves in a mass of glutinous matter that oozes from the small twigs of the tree, and which furnishes them both food and shelter. As they are marvelously prolific, a single female, according to the estimates of entomologists, being succeeded by many millions of descendants in less than a year, when a colony has possession of a tree, every tender branch is soon punctured, and the abundant resinous juices that flow out envelop it in a coating often half an inch thick. These branches, and also what falls to the ground, are collected, and the wax, melted off, is prepared for the market. From this source the shellac of commerce, so extensively used, is obtained. This curious and useful insect, like its congener, the cochineal, secretes a coloring substance, but of different tints, and less valuable. The Lac insect is a native of Siam, Assam, Burmah, Bengal, and Malabar. For some years the average annual imports into Britain have been a little over 600 tons of the lac dye, and more than a thousand tons of lac, including the several varieties. This industry also gives employment to many thousands of people.
METAMORPHOSIS OF A BEETLE.
Ex.—A, larva; b, pupa; c, beetle.
IV.—Coleoptera[20] (sheath-winged). Beetles are innumerable, about ninety thousand species being recognized. Their anterior or upper wings, useless for flight, are composed of a hard, horn-like substance known as chitine, and meet in a straight line on the top of the back. The posterior wings are thin, membranous, and, when folded, out of sight. They have usually two pairs of laterally moving mandibles, or jaws, and in their development undergo several metamorphoses. We see the egg, the larva, or grub, in different stages of its growth, the chrysalis, and the imago,[21] or complete beetle. Entomologists have spent much time and labor in making collections, and classifying them according to their peculiarities of form or habits. If many are repulsive, and most plain in form and color, some are beautiful, and worthy of our admiration. Beetles, especially in their larva stage of development are very voracious, and as most of their species live on fruits, leaves, and stems of plants, they are often destructive of crops, and even of forests. Millions of vigorous, valuable trees have been assailed, and stripped of their leaves fast as they appeared, or literally bored to death. All know the ravages of the potato beetle on our American tuber, that has to be assiduously defended to prevent the entire destruction of the crop. Some known as Goliath and Hercules beetles are large, often measuring six inches in length, exclusive of their long antennæ. The “Diamond beetles” of Brazil are adorned with the most brilliant colors, showing a beautiful metallic luster, and the elytra,[22] or chitine sheaths, of this species are now largely used in the manufacture of personal ornaments.[23]
V. Diptera (two-winged), or Flies, number about 24,000 varieties. Among these are the Mosquito, Hessian fly, Daddy-long-legs, Flea, and common House fly. They usually have one pair of fully developed wings, the second pair being rudimentary, although a few, as the fleas, are wingless. They pass through a complete metamorphosis, the larvæ being usually footless maggots, with the breathing holes in the posterior part of the body; the pupa are either encased in the dry skin of the larvæ or are naked.
VI. Lepidoptera[24] (scaly-winged), or Butterflies and Moths, are distinguished by four wings, covered on both sides by minute scales. The butterflies fly by day and have knobbed antennæ, while the moths fly by night and have feathery antennæ. Among the moths one of the most interesting is that of the silk worm.[25] The physiology of the insect and its metamorphoses reveal nothing very peculiar, and its habits need not be mentioned farther than to say, the larva eats voraciously, with short intervals of abstinence, until full grown, which stage is reached in about a month. During the last ten days the silk germ is elaborated, the eggs laid, and then the spinning and winding soon begin. To complete the cocoon requires at most only about three days. The larva then becomes a chrysalis, and in due time the moth emerges from its cell.
VII. Hymenoptera (membrane-winged) comprises the Ichneumon and Gall fly, Ants, Wasps, Bees, in all about 25,000 species. This order includes the most social of the insects. They have four wings, which in flying they fasten together by means of small hooks on the edges. The females are usually provided with a sting or borer. The Gall fly produces the gall nuts or oak balls so common on oak trees. The Ichneumon fly introduces its eggs underneath the skin of the caterpillar.[26]
Ants[27] live in communities. They are divided into fertile females, males and infertile females. Among the ants, the mining ants, which make long galleries in the earth, and carpentering ants, which perforate solid timber, are the best known classes. Some species, like the white ants of the tropics, the termites, are famous for their ravages.
The bees are divided into queens or females, drones or males, and workers. Each community or swarm has one queen, which lays the eggs. The bee is provided with a formidable sting.
This curious weapon of attack and defense is here magnified with the adjacent parts. It consists of an extensile sheath with two needle shaped darts that are exceedingly sharp. This spear is furnished with barbs near the point, and when it pierces the skin, if thrust with violence, it sometimes remains, not only making the wound more painful, but, having been wrenched from the bee, frequently causes its death. The sting is connected with a little sac containing a poisonous liquid which is thrown into the wound and increases the pain.
STING OF A BEE.
SUB-KINGDOM VIII.—TUNICATA.
This very small class of animals is distinguished by the leathery sac-like covering, from which they take their name of Tunicata (having a tunic). The Ascidian[28] is the best known representative. It is found fastened to rocks, shells, crabs, and other bodies. These animals are both simple and compound; the latter are often phosphorescent. They have neither feet, head nor shell, but a shapeless body with apertures at both ends.
SUB-KINGDOM IX.—VERTEBRATA.
This division includes the most perfect animals. Their chief distinguishing characteristics are an internal skeleton; a backbone; a dorsal nervous cord, separated from the body cavity; a complete circulation, and limbs not exceeding four. There are about 25,000 living species, beside the numberless host now extinct.
Lowest of the vertebrates, and closely related to the true fishes, are the Lancelet and Lamprey.[29] The former is a lance-shaped animal having no skeleton, but boasting the rudiment of a backbone in a string-like cartilaginous cord. The organs are very simple, the heart being a long sac in which colorless blood circulates. It breathes by taking in water through the mouth and letting it out through the gill-slits. The Lamprey belongs to the pouch-gilled vertebrates or Marsipobranchii.[30] It is an eel-shaped animal of about three feet in length.
The round, soft mouth is suctorial, the tongue acting as a piston. By suction it can anchor itself to a rock, and allow the long body to float freely, without being carried by the current from the place. There are seven gill openings on each side, and the whole breathing apparatus so arranged that the animal can live some days out of the water. In some parts of England it is in demand for the table, and “lamprey pie”[31] is esteemed a great luxury. The American lamprey is similar, and the flesh good, but in less demand in our markets. During the breeding season those about the estuaries go up stream as do the shad, and by rolling stones together construct large conical nests[32] for the protection of their young. With apparently little adaptation for such architecture they accomplish wonders in that line.
THE LAMPREY.
Class I.—Pisces. The first clearly defined division of vertebrates is that of the fishes. They are regarded as, in some respects, the lowest of vertebrate animals. They are credited with having the least intelligence and sensibility. Their eyes, though often large, are nearly motionless in their sockets, are protected by no eye-lids, and are without the expression usual even in the animal eye. If they have ears the external parts are wanting. Sounds may reach the auditory nerve and be heard through the cranium. The other senses, as taste, touch and smell, are but slightly developed. But they are admirably adapted to the element in which they live, and the mode of life for which they were created. In no other organisms is the evidence of design in the adaptation of means to the ends contemplated, more apparent. In the number of species and variety of forms they exceed all other vertebrate animals.
The skeleton of a fish is usually divided into four parts: the head, respiratory organs, vertebral column and limbs.
The head is very suggestive, and of itself presents a profitable study. It is not hung or poised on a neck, but attached immediately to the body. In most species it is large, making a large mouth possible, but pointed, to lessen the resistance met in passing through the water. In some the eyes are quite near the nasal organ, in others farther back. In some they face laterally, in others upward. As there is no nictating[33] membrane there is neither winking nor the shedding of tears. Both jaws are, to some extent, movable and provided with osseous teeth that are usually sharp and of a spike-like form.
From the heads here presented the operculum,[34] or gill cover, is removed to show those delicate respiratory organs. The branchiæ, or gills, are situated at the sides of the head just back of the eyes, and consist of numerous and very vascular[35] plates, arranged in double fringe-like rows, fixed or attached at the base only, and so constructed, in all respects, as to expose as much surface as possible. These gills are covered with innumerable small blood vessels, to which blood is pumped from the heart, there to receive the needed supply of oxygen. The oxygen is obtained from what air circulates through the water, and not by a decomposition of the water, as some have supposed. For some species the modicum of oxygen, thus obtained, seems insufficient, and they come to the surface for more.
HEADS OF FISHES WITH GILL-COVERING REMOVED.
Notice another peculiarity. There being no neck or long gullet, the principal digestive organs are packed in the cavity near the capacious mouth, and this leaves the whole of the posterior tapering part of the body for strong muscles, that can vigorously move the caudal extremity from side to side as a propelling oar. The spine is so jointed as to allow a free horizontal and but little vertical motion.
The bones of fishes are less compact than those of the higher orders of animals, but quite elastic; and in some species small bones are distributed through the flesh, giving additional firmness to portions that lack muscular strength. As the peculiar breathing apparatus of the fish is adapted to its element and mode of life, so is every part and appendage of the whole structure. Adaptation reigns through the whole. The elongated tapering body, its scaly covering exquisitely adjusted, the material and position of the fins, all attest the intelligent and beneficent purpose of the Creator.
The Elasmobranchii[36] (strap-gilled) have a cartilaginous skeleton, rough skin, and uncovered gills. The Shark, the Saw-fish and the Ray are representatives of this order.
The Ganoidei (enameled scales) formed one of the largest orders in ancient geological history, but they have now but few representatives, such as the Sturgeon, Gar-pike and Mud-fish. Their characteristics are a skeleton not completely ossified, ventral fins placed far back, and the tail heterocercal, that is, having the upper lobe larger than the lower.
The Teleosti[37] (perfect bone) form the largest order, including nearly all our common fishes. The characteristics of the order are an osseous or bony skeleton; gills protected by a gill cover or operculum; and an equally divided tail. Lowest among the Teleosts is the common eel. It has an elongated, cylindrical, thick-skinned body, and is destitute of ventral fins. There are many species, and they are widely distributed, living in both salt and fresh water. One species is electrical.[38] The cat fishes of this order have long threads hanging from their jaws, and are noted for their peculiar methods of protecting their young; one species is electric, having cells arranged in layers over the body.
Other peculiar types are the Blind or Cave fishes,[39] living in the waters of caves; the Lamp fishes which take their name from the luminous spots arranged along the sides, and which are supposed to light the recesses where they live, and the Flying fishes.
There are at least two genera, and more than thirty species of “flying fish,” a name given to all those which have the pectoral fins so large that they are sustained in short, seeming flights through the air. They do not really fly, as they have not muscular power in their fins to beat the air as birds do. But when extended the fins help bear them up, and the impulse received at the start, sufficient to give them the elevation they reach, may be supplemented by the use of the caudal fin as in swimming. Some naturalists claim to have noticed a movement of the other fins, but the preponderance of testimony is that these are of service only as parachutes or the wings of a paper kite. The Herring, Shad, Salmon, Pike, Perches, Bass, Mackerel and Cod are valuable food fishes, belonging to the Teleosts. The Sword fishes, in which the upper jaw is developed into a long, sword-like projection, used as a weapon of defense and offense, is an interesting member of the order. The Climbing fishes, noted for being able to live out of water, and the Nest Builders, which make homes from the weeds of the Sargossa Sea,[40] are peculiar types.
Another curious Teleost is the Sea Horse. This peculiar animal has its name (Hippocampus) from the shape of the head, that has some resemblance to that of a horse. There is no other resemblance. The short body, without legs, is covered with angular spinous plates. Its fishy part is a long prehensile tail, but it has neither dorsal nor caudal fins.
The last order of fishes is the Dipnoi, or Lung fishes. They are characterized by the possession of two lungs, as well as gills. The gills are used in respiration when the fishes are under water, but when out of it, and burrowing in the mud as they often do, the lungs are put into service. They are also known as mud fishes, from their habits of encasing themselves in the mud.
THE SEA HORSE.
End of Required Reading for May.