THE animals belonging to this subkingdom are specially distinguished by the body and limbs being jointed: as familiar instances, may be mentioned the lobster, the wood-louse, spiders, insects, and worms.

Taking the class Crustacea, to which the two first animals belong, we find interesting microscopic forms in the subclass Entomos´traca (??t???, insect; ?st?a???, shell).

Entomostraca.—The animals contained in this Order are met with in every pool or pond, some of them inhabiting the sea. They are mostly minute, yet visible to the naked eye, forming specks swimming actively or leaping through the water; hence some of them have been called water-fleas. The body of the animal is protected by a shell or car´apace, which in some consists of a single piece (Pl. IX. fig. 30), while in others it consists of two similar parts or valves (fig. 31), in the latter case the joints of the body being indistinctly visible. The head is furnished with usually two projecting feelers or antennÆ (anten´na, a sail-yard), one of which is uppermost or superior (Pl. IX. figs. 30, 31, 34 a), the other lowermost or inferior (figs. 30 and 34 b); and these are often used for swimming. The antennÆ are jointed, and sometimes beautifully plÚmose (pluma, a feather) or feathery, i. e. furnished with rows of long and very slender filaments. There are several pairs of jointed legs, some of which serve as jaws (foot-jaws), while others are finely filamentous to serve for swimming and as respiratory organs (branchial feet). The four species figured are very common.

Cypris tristriÁta (Pl. IX. fig. 34) is found in ponds and ditches. The carapace is bivalve, or has two valves, which are convex and oval; and it is of a greenish colour, with three irregular dark stripes behind. The superior antennÆ (a) are jointed and finely feathery, the inferior antennÆ (b) having a tuft or pencil of fine filaments arising from their anterior margin. The eye is single. The animal swims steadily and freely through the water.

The eggs of Cypris (Pl. IX. fig. 35) are often found in glasses of water containing the animals. They are rounded or oblong, of a red colour, glued together by an amorphous jelly, and adherent to pieces of stick or the sides of the glass. They are enclosed in a thick shell, which exhibits a cellular appearance in the surface view, and is striated in the side view; so that the structure of the shell is prismatic, as in that of the oyster. When the eggs escape from the shell, they present the appearance represented in fig. 35 a, the body of the young animal being enclosed in a transparent envelope, one end of which forms a blunt protrusion; there is also a separate slender process enclosing the superior antennÆ. After a time, the envelope is cast off (fig. 35 b), when the animal begins its active stage of life. The cast-off envelopes (fig. 35 c), with the protruded portions wrinkled, are often found in the sediment of water containing the animals. The structure of these ova is that of what are called winter ova, which agree with the resting-spores of the lower plants or the AlgÆ.

Cy´clops quadricor´nis (Pl. IX. fig. 30) is another common species. In this the body is closely surrounded by the jointed shell, as in a lobster. The superior antennÆ (a) are very long and many-jointed, each joint having short bristles arising from it, while the inferior antennÆ are short and four-jointed. There is no separate head, this being united to or consolidated with the first joint of the thor´ax or chest, the head and thorax together comprising four joints. The remaining joints enclose the belly, or abdÓmen, which has the appearance of a tail; but the tail is constituted by the two last parallel pieces, which are furnished with fine feathery filaments.

The female is most commonly met with, and is easily known by having the egg-pouch, or ovary (o) external on each side, and filled with eggs or ova. The little Cyclops is readily recognized by its form and jerking motion through the water.

Daph´nia pÚlex (Pl. IX. fig. 31) is a very common Entomostracan, and is very well adapted to illustrate the structure, on account of its size and transparence. In this animal the body is loosely connected with a bivalve shell, which, on careful examination, is seen to be reticulated or marked with net-like lines. The superior antennÆ (a) are very small, placed under a small beak, and have at the end a minute tuft of hairs. The inferior antennÆ (b) resemble arms, being large and branched; and by means of them the animal rows itself through the water. The structure of the eye is curious, consisting of a number of round lenses aggregated together, the fine muscular threads by which it is moved being easily distinguished with a high power. The legs are flattened, and furnished with elegant feathery sÉtÆ (seta, a bristle), serving as gills or branchiÆ. They are constantly in motion, fanning the water so as to change incessantly the portion with which they are in contact. About the middle of the back is placed the little transparent heart, with its colourless blood, which may be distinctly seen beating, or contracting and dilating, in the living animal; and between the back of the animal and the shell are seen the ova, which remain there until they are hatched.

The genera and species of the Entomostraca are very numerous. Those mentioned above will serve to illustrate the general structure of the order. To distinguish the man´dibles (mandib´ula, a jaw) or proper jaws, the foot-jaws, and the branchial legs, the animals must be dissected in water with the mounted needles. The very delicate feathery filaments of the branchiÆ may be best observed when these organs are dried on a slide.

The Entromostaca may be kept alive in a jar of water with water-plants for a long period. They may be removed from the water for examination by the dipping-tube, and are best observed in a live-box.

Arach´nida (??????, spider) is the Class of spiders, scorpions, and mites.

AranÉida.—This Order contains the more highly developed forms of the Class, among which are the common spiders of houses and gardens; and some of their structures are very curious and interesting.

The head of spiders is united or fused with the thorax, forming one piece, which is called the ceph´alothorax (?efa??, head, ???a?, chest).

The claw-jaws, or man´dibles, are terminated by a curved and pointed claw, with which the spiders hold their prey. It is traversed by a slender canal, containing a slender tube or duct leading from a poison-gland, and opening near its point; and when the insect prey is transfixed by the mandible, the poison is pressed out and enters the wound.

Near the root or base of the mandibles on each side is a jointed feeler, or pal´pus; but spiders have no anten´nÆ. The eyes are simple, forming separate round shining dots, and are called ocel´li (ocel´lus, a little eye); they are usually placed on the top of the head, and are often arranged in a geometrical form, as a triangle, &c.

The legs are four pairs; they are hairy, and terminated by two or three claws, which are fringed with minute teeth, or pec´tinate. These claws serve to comb the fibres of the web, just as we comb our hair with a common comb.

The spinnerets, with which spiders form their web, are very curious organs. They are situated at the under and hind part of the body, and consist of two or three cones, or papillÆ, on each side. On the summits of these papillÆ are very numerous bristle-like tubes, through which the secretion of certain glands passes; this secretion, when hardened by exposure to the air, forms the fibres of the web.

On carefully examining a spider’s web, the radial fibres, or those which pass from the centre to the circumference, will be found to be smooth, these fibres serve to fix the web; while the cross fibres are covered with numerous viscid globules, which serve to attach flies or other prey to them. This difference of the fibres is best observed with a hand-lens.

AcarÍna, or the Order of Mites.—Here belongs cheese-mite, Ac´arus domes´ticus (Pl. IX. fig. 36). Its body is somewhat milky white, oval, and furnished with feathery hairs. When viewed from beneath, there is seen a transverse line, indicating the separation of the thorax from the abdomen; and another line in front of this, with four minute tubercles, from each of which arises a hair. The head is pointed and beak-like, forming a ros´trum (rostrum, a beak), consisting of two mandibles pressed together; these can only be seen to be separate when dissected apart with the mounted needles. Each mandible is chÉlate (????, forceps), or has the form of a lobster’s claw; and beneath the two mandibles is a flat membranous under lip or labium, consolidated on each side with a palp. The legs are four pairs, as in all the Arachnida; they are pinkish, 6-jointed, and terminated by a leaflike sucker and a minute claw.

The males (fig. 38) are smaller than the females, the fore legs being much stouter, and furnished with a blunt tooth (fig. 38 a). The eggs can often be distinguished within the body of the female (fig. 36); they are oval and granular.

Another species of Acarus, A. sac´chari, is found abundantly in ordinary moist sugar. If a little of the sugar be placed in a wine-glass, some water added, and the mixture be stirred until the sugar is dissolved, the Acari will be found both in the sediment and floating on the surface.

A somewhat larger member of the order occurs as a parasite upon a species of Dung-beetle (GeotrÚpes stercorÁrius) which is vulgarly known as the Lousy Watchman. The beetle is black, shaded with purple, about three-quarters of an inch long, and is found under cow-dung. The mites cling pertinaciously to the under parts of the beetle, and can easily be seen with the naked eye. They are whitish, with the mandibles, the sucker, and two claws very distinct; and the palpi are unattached to the labium, or free. These mites form the species Gam´asus coleoptrator´um. Another species, Gamasus telÁrius, is the red spider of the greenhouse.

Trombid´ium fuliginÓsum (Pl. IX. fig. 37 d) is a common red spider of gardens. It is of a scarlet colour, appearing velvety from the presence of a dense coat of feathery hairs (fig. 37 f). The palpi of this mite are large, free, the last joint but one (Pl. IX. fig. 37 a) being furnished with a claw, while the last joint is obtuse, and resembles a lateral appendage. The mandibles (fig. 37 b) are furnished with a sharp curved claw. The legs are long, especially the anterior pair, and terminated by two claws, with a delicate sucker-like appendage (fig. 37 c).

Another species of Trombidium, T. holoseric´eum, greatly resembling the last, is also found in gardens. It may be easily distinguished from the last by the club-shaped hairs (fig. 37 e) existing upon the body. The harvest-bug, which causes such irritation of the legs of persons who frequent corn-fields in the autumn, is also a species of Trombidium—T. autumnÁle.

Preparation.—The organs of the mouth, &c., of the Spiders are easily prepared for examination, by carefully pulling them off with forceps or the mounted needles, then drying them under pressure between two glass slips, macerating in turpentine, and mounting in balsam. Those of the Acarina should be dissected out with the needles, after the body has been crushed in a drop of water on a slide, and the internal substance has been gently washed away with a hair pencil. They may then be dried on a slide, with a cover laid on, and turpentine applied to the edge of the cover, balsam being added when most of this has evaporated. The various parts may also be mounted in chloride of calcium or glycerine.

Insects.—The members of the class of Insects are extremely interesting to the microscopic observer, not only on account of the beautiful structures which they present, but also from these being comparatively large, usually coloured, and easily distinguished under the lower powers. Hence they form admirable objects for study to those who are but little accustomed to the use of the microscope.

Myriap´oda (?????, myriad, p???, foot).—This Order contains those insects which are popularly known as the hundred-legs and millepedes; by many zoologists they have been arranged in a distinct class.

The most common member of this Order is LithÓbius forcipÁtus (Pl. X. fig. 4), which is found under stones, in cellars, and among garden-rubbish. It is of a yellowish-brown colour, with long, many-jointed, gradually tapering or setÁceous (sÉta, a bristle) antennÆ (figs. 4 a, 5 a), and two large and powerful mandibles (fig. 5 b) resembling those of the spiders. It has also a broad, notched, and toothed lower lip, or labium (fig. 5 d), above which are two toothed jaws, or maxillÆ, and two lip-feelers, or labial palpi (c). The eyes consist of a group of ocelli on each side (e). The body is protected by alternately larger and smaller dorsal plates, which are fifteen in number; and there are fifteen pairs of legs, which are terminated by a single claw. On the sides of the body will be found some oval dark-looking bodies, fringed with hairs; these are the spir´acles (spirac´ulum, a breathing-hole) or breathing-pores. They form the orifices of certain branched and transversely striated tubes, which are distributed throughout the body; the tubes are called trÁcheÆ (trachea, the windpipe), and their walls contain an elastic spiral fibre which keeps them open. These parts of the insect can only be distinctly seen when the body has been slit up on the under side; and, after washing away the animal matter with water by the aid of a hair pencil, pressed between two slides with a clip, dried, soaked in turpentine, and mounted in balsam.

ThysanÚra (??sa???, fringe, ????, tail).—The insects belonging to the genus PodÚra, of this Order, are very minute and difficult to examine; but they are specially interesting, on account of the structure of their scales. They are common in gardens and cellars, under flower-pots, &c., and are about one-tenth of an inch long. They are of a brownish or silvery-leaden colour, wingless, with six legs, and when touched they leap like a flea. The leaping motion is produced by the action of the tail, which is forked and bent under the body.

The body is usually covered with minute scales (Pl. X. fig. 19, a, c), and these are used as test-objects. The structure of the scales varies in the different genera and species; those usually used (fig. 19 a) are stated to belong to PodÚra plum´bea; it appears, however, that this is not correct. The scales sold as test-objects under this name are covered with minute and short raised lines (fig. 19 a), arranged in irregular but somewhat parallel wavy rows. It requires a good microscope and a high power to show them distinctly, and they should appear perfectly black and separate. The little lines are much coarser in some scales than in others; so that there are easy and difficult scales, as they are called.

The PodurÆ may be caught by holding a sheet of paper near their haunts and disturbing them; and when they have jumped upon the paper, a slide laid upon them and gently pressed will remove some of the scales for examination.

The scales should be mounted as dry transparent objects; for if wetted, they become very transparent, and the markings appear removed, which however is not really the case.

The scales of Lepis´ma saccharÍna (Pl. X. fig. 19 d), a member of this Order, were formerly used as test-objects; but they are too easily made out to serve for this purpose with modern microscopes. The insect is not common. The scales (fig. 19 d) exhibit continuous nearly parallel longitudinal lines or ribs.

AnoplÚra (???p???, unarmed, ????, tail).—This third Order of insects consists of the Lice of the Mammalia and birds. They are minute, resembling mites to the naked eye, but may be at once distinguished from them by the distinct head and thorax and the presence of six instead of eight legs.

Some of them are suctorial, i. e. have a short and slender tube, with which they suck the blood of the animals of which they are parasites; while others are mandibulate, or have mandibles, and also maxillÆ, their food consisting of portions of feathers, hairs, and scurf. The legs are usually short and stout, and the claws large and powerful, to enable them to hold firmly to the hairs, &c. The Anoplura are most abundant on dirty and diseased animals.

Suctor´ia.—The fourth Order of insects consists of the genus PÚlex,—Pulex irrÍtans being the human flea. Other species are found upon different animals, as upon the dog, the rat (Pl. X. fig. 22), the fowl, the pigeon, &c.

The head and the dark eye (fig. 21, head of the human flea) are very evident. The antennÆ or head-feelers are very minute and difficult to find, being sunk in a little pit or fossa behind the eye; they may, however, generally be recognized by the detection of the last joint, which is pectinate or cut like a comb. The body, including the head, consists of thirteen joints, one for the head, three for the chest or thorax, and nine for the belly or abdÓmen,—it being understood that by “joint” is meant a segment, and not the line of junction of two segments. The indication of these joints is afforded by the horny integument, which consists of a corresponding number of rings, forming in fact the skeleton of the animal. This in the flea, as in all insects and other Articulata, is external or cutaneous (cÚtis, skin), and consists of the hardened skin, the peculiar animal substance of which it is composed being called chitine (??t??, tunic). These chitinous rings overlap, and are composed of a dorsal or upper, and a ventral or lower half; and near the middle of each is a row of hairs directed backwards. Along the sides of the body of the insect may be seen a row of dots; these are the spiracles or orifices of the breathing-tubes (tracheÆ).

The legs are many-jointed, long, furnished with numerous spines, and terminated by two slightly curved claws, each with a little blunt tooth at its base. The claws are not perfectly smooth on the inside, but are covered with slightly raised lines, like a file, so that a better hold can be taken of bodies.

But the most interesting parts of the flea are those of the mouth, with which it punctures the skin and sucks the blood. There are nine of these; and they are best seen when the head of the flea is pulled off with the mounted needles, and the parts spread out and mounted in balsam, a high power being used to examine them. One of them forms a long and slender bristle (seta) or tongue, furnished with distant minute teeth. On each side of this is a flattened seta, with two rows of teeth on the edges; these are the lancets, and when not in use these organs are inclosed in two jointed sheaths. Outside these are two representatives of jaws, or maxillÆ (b), each having a jointed feeler or palp (a) arising from it; the probable use of the palps being to feel the position of the skin, so that the animal may be able to adjust the lancets at a proper distance for puncture.

The eggs of the flea are often visible within the body of the parent; and when this is crushed, they are more distinctly seen, of various sizes, and contained within a long tube, which is the ovary or egg-bag. The eggs are laid by the animals upon carpets, woollen garments, or in the cracks of dirty floorboards; they are just perceptible to the eye as white oblong specks, and they may always be found on the rug when a cat is kept in the house. When hatched, they give rise to a minute white worm-like maggot, or larva (fig. 30), having a 12-jointed body, with two rudimentary antennÆ and two slightly curved hooks appended to the last joint. The mouth-organs of the larva are adapted for biting, and not for sucking, as in the perfect animal, the jaws or maxillÆ being distinctly toothed. When they have acquired full growth, which takes place in about twelve days in warm weather, they spin around themselves a little silky cocoon, and become transformed into a chrysalis or pupa; and from this, in about a fortnight, the perfect insect escapes.

Dip´tera (d??, twice, pte???, wing).—This, which forms the fifth Order of Insects, consists of the two-winged insects, or flies, as the house-fly, the blue-bottle, the gnats, &c.

Mus´cidÆ.—The house-fly, and the blue-bottle or meat-fly, are both species of the genus Mus´ca, belonging to this family, the former being Musca domes´tica, the latter Musca vomitor´ia. Both these insects are seen to be wonderfully constructed when minutely examined, and they possess considerable resemblance in general structure.

On examining the head of the house-fly (Pl. X. fig. 17) under a low power, and as an opake object, the observer will be struck with the remarkable appearance presented by the two eyes, which are large, placed one on each side of the fore part of the head, and composed of very numerous little eyes closely packed together, or they are compound, as it is called. The use of this compound structure is evidently to enable the little animal to see in all directions without moving the head and eyes. Each little eye has a lens to bring the rays of light emanating from objects to a focus upon a nerve. The packing of the eyes together gives rise to their angular form or their straight sides, each of the little surfaces or facets being hexagonal, or bounded by six sides (fig. 33). In front of and between the eyes are seen the two small antennÆ; these have three joints, the third of which is larger than the rest (fig. 17 a), and arising from near its base is a feathery bristle or seta; these structures are best seen when the antennÆ are pulled off with a pair of forceps and mounted separately. Below the antennÆ, and extending downwards and forwards is the proboscis, or tongue, as it is called, which can be entirely retracted within a pit in the fore part of the head, or protruded at the will of the animal. This is a very beautiful and complicated instrument, and is best examined when spread out and separately mounted (Pl. X. fig. 29). It consists of a fleshy tube, dilated at the end into two lobes, which are flattened beneath to form a sucking-disk. The end is furnished with two solid horny lateral branches to keep it expanded, and with two longitudinal tubes beneath, running parallel, from the outer sides of which arise numerous nearly parallel branches. These tubes and their branches are incomplete beneath, and consist of imperfect rings, otherwise greatly resembling tracheÆ. On each side of the proboscis is a lip-feeler or labial palpus, for the organ represents the labium of other insects. All these parts are better seen in the proboscis of the blow-fly than in that of the house-fly, on account of their larger size. The head, the thorax, and the abdomen are very distinct in the fly, being separated from each other by well-marked constrictions.

The legs are composed of five parts, each having a separate name. The first piece or joint, which is that attached to the body, is called the hip, or coxa; the next is a very small, somewhat triangular piece, and is the trochan´ter; next comes the long and stout thigh, or fÉmur; this being succeeded by the tib´ia, which, as in most insects, is furnished with strong spines at the end; and lastly is the foot, or tar´sus, consisting of five joints, the three last of which are represented in the figure (Pl. X. fig. 32). At the end of the fifth or last joint of the tarsus (fig. 32) (for it must be noted that the joints of the limbs of insects are always numbered in order of distance from the body) are two soft little cushions, or pulvil´li, which are covered on the under surface with numerous hair-like bodies dilated at the end, acting as suckers in enabling the fly to adhere to smooth surfaces. In addition to these organs are two curved claws, and between them a sharp straight spine.

The eggs of the fly are deposited upon heaps of decaying animal and vegetable matters, as dungheaps, &c. The blow-fly deposits its eggs in the same situations, but especially those where the animal matters are most abundant: every one knows the eggs as deposited upon tainted meats, when they are called flyblows. When the eggs are hatched, the larvÆ or maggots make their appearance. The larvÆ of the blow-fly are well known to the angler, who uses them for bait, and calls them gentles.

These larvÆ exhibit some interesting points of structure. The jointed or ringed condition of the body is distinct to the naked eye. The head is provided with two rudimentary palpi, placed each upon a rounded papilla; also with two brown curved and horny hooks or jaws. On the posterior end of the body are two brown spots, which consist of spiracles, and have three sieve-like oblong orifices; and at the anterior margin of each segment of the body are very numerous little short spines, with the points directed backwards. These answer the purpose, to some extent, of legs; for when the larva is moving, and has forced itself through the matter in which it burrows, the little spines prevent the body being forced backwards as the head is pushed forwards and meets any resistance.

To examine the structure of these larvÆ, the gentles should be killed by immersion for a time in warm water, and then dried by touching them with blotting-paper. The hooks and palpi can be seen by holding the body in the forceps as an opake object. To observe the spiracles, the end of the body should be cut off, and the animal matter washed away in a watch-glass with water and a hair pencil, then spread out, dried between two slides, and mounted in balsam.

The larvÆ of the house-fly and of the blow-fly very closely resemble each other, so much so that the former are generally overlooked; hence it is often wondered where flies come from, although they are so numerous in every house. When the larvÆ of these flies are fully developed, they gradually assume a brown colour, the organs of the head are retracted, and the skin becomes dry and hard. This is the state of pupa, or chrysalis; and while remaining in this state of rest, the development of the wings, legs, &c., takes place; so that when the insect emerges from the shell of the chrysalis, it has attained its highest state of development, and forms the imÁgo or perfect insect. It may be remarked here, that when insects pass through the three states of larva, pupa, and imago, they are said to undergo complete metamorphosis. There is not a more curious object than that presented by the young fly contained in its case, as seen on carefully cutting away portions from one end of the case of the chrysalis. The body and head are quite white, with beautiful blood-red eyes.

Most persons must have noticed another kind of house-fly, having the wings more widely separated than in the common fly, and moving more slowly through the air. This is Stomox´ys cal´citrans. The proboscis of this fly (Pl. X. fig. 18) differs from that of the house-fly in being longer, more bent, and but little expanded at the end; also in being provided with two long setÆ, one forming a slender sharp lancet, the other being somewhat stouter, and forming its sheath. The fly is thus enabled to pierce the flesh and suck the blood.

Culic´idÆ.—We will now say a few words about the gnats, which are old favourites for microscopic examination. The three states of larva, pupa, and imago must be considered separately.

The imago or perfect form is well known. The males are easily distinguished from the females by the difference in structure of the antennÆ, which in the males (Pl. X. fig. 10, head) are very beautifully plumose or feathery, whilst in the females (fig. 11) the hairs are very short—the long proboscis, or rostrum, or bundle of biting-organs forming the striking feature; this difference is immediately evident to the naked eye.

The antennÆ of the males (fig. 10 a) consist of numerous small joints, from each of which arises a ring of long hairs, giving the appearance of a tuft on each side when flattened for view as a transparent object under the microscope; at the end are two longer joints, the first having a small ring of shorter hairs.

The proboscis of the female is a very complicated organ, consisting of six separate bristle-like pieces or setÆ, all nearly of the same length. Two of these are somewhat curved near the end, and provided on the inside with fine teeth; another pair consists of very thin lancet-pointed instruments; then comes another lancet-pointed seta, very sharp at the end, and traversed by a canal; next, a stouter and darker-looking tube, slit up underneath, which serves to contain the two toothed setÆ; and lastly, a stout and broader sheath, also slit up throughout its length beneath, in which all are packed. This sheath has two lobes at the end, and has some resemblance to the proboscis of the fly, of which organ it is the representative.

The gnat lays its eggs in water. The eggs are longish oval, with a kind of neck at the upper end; they are glued together side by side in large numbers, and form a boat-like mass, floating on the surface of the water. The larvÆ (Pl. X. fig. 9) are very commonly found skipping through the water, or hanging, as it were, by the tail from the surface. The head is very broad; and arising from each joint of the body are tufts of hairs. Near the end of the body is a tube which communicates with the tracheÆ; and when the animal is quiet, this tube is brought to the surface; so that when the animal appears hanging to the surface, it is breathing. In addition to this method of respiration, there are other respiratory organs attached to the last joint of the body, consisting of leaf-like plates; hence these larvÆ have an aquatic as well as an aËrial respiration: the respiratory or branchial plates also serve as a tail to aid in swimming. Running down the back of the larva will be seen a thin delicate vessel, dilated opposite the thorax, and beating or contracting at regular intervals. This is the dorsal vessel, the dilatation representing the heart of the higher animals; and it serves to propel the colourless blood throughout the body.

After several moultings or castings of the skin, to allow of the growth of the insect (for insects grow only in the larval state), the larva becomes transformed into the pupa (Pl. X. fig. 8). In this state the animals still move about in the water, and are often found suspended from its surface by two respiratory tubes, which, however, are not connected with the tail, but arise from the thorax; and the various parts of the perfect insect may be seen through the case or skin, within which they are closely packed.

When the pupa has attained its full development, the perfect insect emerges from it, leaving the water to fly about and seek food.

Tipu´lidÆ.—In the water of ponds and pools a young larva (Pl. X. fig. 31) will often be met with, which is that of Chiron´omus plumÓsus, a largish gnat-like insect, belonging to the daddy-long-legs family (TipulidÆ). This larva exhibits the usual thirteen segments, including the head. In the young state the body is nearly colourless; but in the mature larva it is of a blood-colour, and about an inch in length. Beneath the first joint of the body are two foot-like processes covered with hair; and at the end of the body are also two processes, surmounted with hooks. The three last joints of the body are also furnished each with a pair of fleshy processes, those of the first pair being very short.

Hymenop´tera (???, membrane, pte???, wing).—This, which forms the sixth Order of insects, contains the bee, the wasp, the ant, &c.

In the Hymenoptera there is a curious contrivance for linking the two wings on each side, so that they may form a single piece in the flight of the insect. It consists of a row of hooks, placed upon the anterior nerve of the hind wing, which play upon the folded-in corresponding edge of the fore wing; the hooks, sliding along this edge, allow of freedom of motion, although still holding the two wings together. This structure may be well seen in the wings of the Humble Bee when mounted in balsam.

The sting of the wasp and bee is also a singular organ. In both insects it is much alike, consisting of a sheath, slit up beneath, in which are contained two long setÆ, or lancets, with bent-back (recurved) teeth near the end. These setÆ are inserted into the flesh during the act of stinging, and at the same time the poisonous secretion from two glands is forced into the wound, which causes the severe pain resulting from the sting.

In the wingless neuters of the common ant, attached to the end of the tibia (Pl. X. fig. 34 c) is a beautiful pectinate process, somewhat resembling a comb (fig. 34 a).

Lepidop´tera (?ep??, scale, pte???, wing).—This Order contains the butterflies and the moths, the entire bodies of which are covered with minute scales. When the insects are handled, these scales adhere to the fingers as a fine dust; and on pressing a slide against the insects, they may be removed for examination. They consist of a very slender and short quill, by which they are attached, and a flattened plate of various forms (Pl. X. fig. 19, b, f); it is, however, generally narrower near the quill, and expanded towards the free end, where it is often cut into lobes or toothlike segments. The scales are usually covered with continuous longitudinal lines or ridges, with granules of colouring-matter (pigment) situated between the two thin layers of which the scales consist. In some of them the form is that of a filament, either simple or branched at the end (fig. 19 e), when they resemble minute hairs. In the males of the large white Cabbage Butterfly (Pi´eris brass´icÆ), certain of the scales of the wings are covered with longitudinal rows of very minute dots (fig. 19 f), and have little tassel-like bodies at the end. The males may be distinguished from the females by the front wings having no black spots, while those of the females have two upon each wing. When the scales are examined as they exist upon the wings of the Lepidoptera, they are found to be imbricated (Pl. X. fig. 3) or overlapping each other like the tiles on the roof of a house.

The Lepidoptera suck the honey of flowers by means of a spiral tongue (Pl. X. fig. 20 c) or ant´lia (antlia, a sucking-tube); this consists of two halves, which represent the maxillÆ of other insects; and their margins are fringed with little tassel-like bodies, probably organs of taste. The antennÆ (fig. 20 a) are many-jointed, clubbed at the ends (d) in the butterflies, and simple in the moths. The palpi (fig. 20 b) are short and densely covered with scales. In the large eyes the facets are very distinct and suitable for examination.

The larvÆ are well known as caterpillars. They have six legs, as in the perfect insects, but rudimentary and with single claws; also some additional pairs of pro-legs, as they are called, with a crown of hooks, towards the hind part of the body. The spiracles of caterpillars are very favourable for observation.

Neurop´tera (?e????, nerve, pte???, wing).—This Order contains the Dragon-flies (LibellÚlidÆ), the Day-fly (Ephem´era), &c., in which the wings are usually so large and so beautifully netted. The species figured (Pl. X. fig. 1), which is wingless, is very common in old books and in collections of dried plants. It is whitish, mite-like, with setaceous many-jointed antennÆ, 3-jointed tarsi, and very broad thighs (femora). Its name is At´ropos pulsator´ius.

Hemip´tera (??s??, half, pte???, wing).—This Order contains the bugs and other noxious insects. Those which we shall notice are the species of A´phis, commonly known as Plant-lice and Green-fly, which are found too frequently upon unhealthy plants. The species figured (Pl. X. fig. 2) is that of the geranium (Pelargonium). The head is small and notched or emarginate. The body is oval and furnished behind with two prolonged tubercles, these being covered with scales, giving them a somewhat striated appearance (fig. 2 b). The antennÆ are 6-jointed (c), the second joint being very small, the last joint long, excavated on one side, and ringed: these organs are reflexed over the body in the natural state. There are two compound eyes, and three simple eyes or ocelli, forming a triangle on the top of the head. The proboscis or rostrum is bent under the body, 4-jointed, and contains three setÆ, two of them forming very slender lancets. The legs are long; the tarsi (fig. 2 a) 2-jointed, the first or basal joint being very minute, and the last furnished with two claws.

In a colony of these insects, some are winged and some wingless; those without wings being usually in the larva state, the pupÆ having rudimentary wings, and the males and females usually perfect wings. Aphis brass´icÆ is the destructive turnip-fly.

Coleop´tera (???e??, sheath).—This, which is the last Order to be noticed, contains the Beetles, so easily recognized by their hard and horny fore wings or wing-cases. The parts of the mouth in these insects are exceedingly well adapted for examination; and as they are not fused or consolidated with each other, they serve to illustrate the typical constitution of the organs as existing in these animals.

Pteros´tichus (Ster´opus) mad´idus (Pl. X. fig. 23) is common in cellars and gardens among vegetable rubbish. The body of this beetle is shining black, the head projecting; the antennÆ (fig. 23 a) are filiform, and compressed towards the end. The thorax is somewhat rounded, with a deep rough pit and a longitudinal stria at each posterior angle. The wing-cases, or elytra, are longitudinally striated; the wings, which in most beetles are concealed beneath the elytra when the insects are at rest, being absent. The tibiÆ of the fore legs are notched on the inside (fig. 24 a), a fringe of hairs being situated in the notch; the tarsi are 5-jointed (fig. 24 b), the first four joints being triangular, the last elongate and terminated by two curved claws. In the male the three first joints of the tarsi of the anterior legs (fig. 24 b) are dilated and heart-shaped.

The parts of the mouth (which are named after an analogy with those of the higher animals) consist of the following pieces:—An upper lip, or lÁbrum (fig. 25 a), which is squarish (quad´rate) and slightly notched; a quadrate lower lip, or lÁbium (fig. 27), with a process on each side, and two 4-jointed lip-feelers or labial palpi (b); and below the labium is a chin, or mentum (fig. 27 a), with a projecting bifid tooth: these parts form the roof and the floor of the mouth. Next come the man´dibles (fig. 26), one on each side, which are stout, curved, and pointed; beneath which are the maxil´lÆ (fig. 28), also one on each side, and provided with a fixed claw (a), ciliated on the inside, and furnished with two pairs of jaw-feelers, or maxillary palpi, the inner (b) being 2-jointed, while the outer (c) are 4-jointed. It will be noticed that the jaws work laterally, or from side to side, and not perpendicularly as in the higher animals.

These parts may be found in most beetles which the observer may submit to examination, being however somewhat modified in different genera. We may consider those existing in the Lady-birds, or species of Coccinel´la, by way of comparison. The body in these insects is very convex, and the head sunk deeply in the thorax. The antennÆ (fig. 15) are short, clubbed (clÁvate), and compressed. The thorax is short and lÚnate, or half-moon shaped. The mandibles (fig. 13) are curved, bifid at the apex, and with a tooth on the inside near the base. The labrum (fig. 14) is transverse, or broader than long. The labium (fig. 12) is furnished with two palpi, which are 3-jointed. The maxillÆ (fig. 16) are two-lobed, the lobes (b, c) being ciliated, and the 4-jointed palpi (a) have the last joint large and hatchet-shaped.

Coleopterous insects undergo complete metamorphosis, the larvÆ being commonly known as grubs. The larvÆ of the aquatic beetles will often be met with in the water of ponds or ditches, especially that of the common large water-beetle (Dytis´cus marginÁlis), or water-boatman as it is called (Pl. X. fig. 7), and in various stages of growth. The structure of the mouth-organs (fig. 6), which are, however, imperfect or rudimentary in some parts, can be readily made out; and their names may easily be found by comparison with what has been stated in regard to the organs of the perfect beetle.

Examination, &c.—The means of catching insects will readily occur to the reader. A bag-net made of a curved piece of cane, to which is fitted a bag made of net, will serve to catch those which trust to flight for escape from their enemies, such as the Lepidoptera; and these may be killed by firm pressure of the thorax between the finger and the thumb. The running insects, as the beetles, may be caught in a spoon or with forceps; and they may be killed by immersion in boiling water or in camphorated spirit. In an excursion, most insects may be carried in a well-corked bottle containing a little wool and a lump of camphor, which stupifies them. When the insects are dead, the limbs should be extended into the natural position by means of pins, the insect being transfixed by a pin run through the thorax or one of the elytra and extending into a sheet of cork. To preserve them, they may be kept in a box, the bottom of which is covered with sheet cork, into which the pins are stuck.

The smaller beetles, &c., which cannot be transfixed with a pin, may be mounted as opake objects upon slips of card, the legs &c., being carefully spread out, and gummed in position with a strong solution of gum-tragacanth in boiling water. Many of the smaller Curculion´idÆ or diamond-beetles, in which the labium forms a rostrum or beak, with elbowed or half-bent antennÆ, form beautiful opake objects when thus mounted, on account of the brilliant scales with which they are covered.

There are two ways of examining insects—either in the entire state as opake objects or the separate parts mounted as transparent objects. In the former case the pin with which the insect is transfixed should be stuck into a slide made of cork, and this laid upon the stage, or the pin may be held by the forceps. In this way, with the use of the side condenser and a low power, the general form and arrangement of the parts of the insect can be made out. The more minute details must be searched for in the individual organs which have been picked off with forceps, and mounted in balsam.

If it be required to submit the parts of a dried insect to examination, this must be previously soaked in warm water for a time, as the legs, &c., become very brittle when dry, and are thus easily injured.

Rotator´ia (rÓta, a wheel) or Rotif´era (rota and fero, to bear).—The animals contained in this class are minute, being just distinguishable to the naked eye as white specks. They are common in long-kept infusions and among ConfervÆ in the water of pools and ditches. Their body is usually longer than broad, often presenting indications of rings; and at or near the posterior end is frequently found a prolongation resembling a tail, but terminated by two short moveable thumb-like processes, rarely a sucker, which enable the animals to cling to objects. The most characteristic organ, however, is a kind of rounded or oval disk, placed at the anterior end of the body, and furnished with cilia. When these are in active motion, the organ appears as a revolving wheel, whence the name of Wheel-animalcules, by which they are sometimes designated. The wheel-organ enables the animals to swim through the water, and also brings their food to the mouth by the currents which it produces. It is usually cleft into two or more lobes, and can be retracted, as is commonly the case when the animals are disturbed.

In many of these animals the body is more or less covered by a horny shell or carapace; and in some it is fixed at the bottom of a tube, within which it can be withdrawn. On the anterior part of the body are frequently seen two or more red spots, which represent eyes. The alimentary canal is mostly distinct, being indicated by the colour of its contents, and it is lined with cilia. Towards its front portion is a gizzard (Pl. XI. fig. 2 a) containing teeth, which are sometimes attached to a jointed jaw-like framework; these are usually in active motion. No heart or blood-vessels have been observed in the Rotatoria; but on each side of the body in many of them is a long wavy tube, containing at intervals minute ciliated bodies, the cilia propelling the water through the tubes, and so exerting an aËrating or respiratory function. The reproduction of the Rotatoria takes place by the formation of ova, which may often be distinguished within the body of the parent.

Rot´ifer vulgÁris (Pl. XI. fig. 2) is a common species. It has a spindle-shaped body, which is capable of contraction almost into a ball. The front or head end is sometimes protruded (fig. 2), at others retracted and obscured by the exserted disk (fig. 2*); and beneath it is a tentacle-like organ, supposed to represent an antenna (fig. 2 b). The position of the jaws is indicated at a. The alimentary canal is seen running down the body; and two ova exist, one on each side of it, these being often recognizable by the existence of the eyes and jaws. At the end of the body are two lateral processes, and a tail-like piece, which can be withdrawn or protruded and is furnished with two moveable portions or toes.

PterodÍna pat´ina (Pl. XI. fig. 3).—This species has a shell or carapace on the back, a two-lobed rotatory organ, two eyes, and a slender wrinkled tail ciliated at the extremity. The curved alimentary canal, and the two strong muscles inclined at an angle, are easily distinguishable.

FlosculÁria ornÁta (Pl. XI. fig. 4) is a very beautiful member of the Rotatoria, and is found adhering to ConfervÆ and other water-plants. The body is club-shaped, and contained in a transparent tube, the ringed narrower portion being fixed to its base. The rotatory organ is divided into five or six lobes, furnished with long, slender, radiating tentacular filaments; these are not vibratile like ordinary cilia, but can be slowly moved. In the contracted state, the filaments form a pencil-like bundle.

Examination, &c.—The Rotatoria are best examined in the living state, the drop of water in which they are viewed being very small, so that their movements may be impeded; and while they are struggling to escape, the various parts of the body will come into view. Their preservation has been attempted by drying on a slide; but when dead they become so contracted and altered, that it is difficult to make out their structure. Should the observer wish to record any observations on their reproduction or habits, it will be well to preserve a specimen of the jaws and teeth, as the species might be with certainty identified by careful examination of their minute structure.

EntozÓa (??t??, within, ????, animal).—This class consists of the parasitic worms, as the Tape-worm (TÆnia), the Thread-worm and Round-worm (As´caris), which live within the bodies of man and animals. It also includes the microscopic eel-like animalcules (species of Anguil´lula) which are found in sour paste (A. glÚtinis), in vinegar (A. acÉti), and in blighted wheat (A. trit´ici). Some of the species of allied genera are met with in damp moss and in the dÉbris or fragments of vegetable substances decaying in water. The general appearance of the microscopic species is that of a minute colourless eel, writhing in the water (Pl. XI. fig. 1). Their internal organs are difficult to distinguish. The alimentary canal is usually evident, and dilated into a kind of stomach, containing near its commencement some rod-like or otherwise-formed teeth. In the species figured there are two apparently tubular lancets, which are capable of protrusion, and evidently serve to wound the prey.