Neurop´tera (νεῦρον, nerve, πτερὀν, 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 (ἤμισυς, half, πτερὀν, 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 (κολεὀς, 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.