In various groups of the Hexapoda - aphids and some flesh-flies (Sarcophagi), for example - the egg undergoes development within the body of the mother, and the young insect is born in an active state; such insects are said to be " viviparous.".
The extreme of this " division of labour " is seen, in those insects whose jaws are vestigial in the winged state, when, the need for feeding all behind them, they have but to pair, to lay eggs and to die. During the pre-Linnaean period, the beauty of insects - especially the Lepidoptera - had attracted a number of collectors; and these "Aurelians" - regarded as harmless lunatics by most of their friends - were the forerunners of the systematic students of later times. The Hemimeridae include the single genus Hemimerus, which contains only two species of curious wingless insects with long, jointed cerci, found among the hair of certain West African rodents. In the Mesozoic rocks (Trias and Lias) there have been discovered remains of insects intermediate between those ancient forms and our modern cockroaches, the differentiation between forewings and hindwings having begun. As the light faded from the treetops, the birds grew silent and insects began their orchestra of night sounds. The families are the Acridiidae and Locustidae - including the insects familiarly known as locusts and grasshoppers (q.v.) The Orthoptera are an exceedingly interesting order of insects as regards their past history. The insects comprised in it are distinguished from the earwigs by their elongate, rather narrow forewings, which usually cover, or nearly cover, the abdomen when at rest, and which are firmer in texture than the hindwings. The various species of rapacious animals are disappearing, together with the colonies of marmots; the insectivores are also becoming scarce in consequence of the destruction of insects; while vermin, such as the suslik, or pouched marmot (Spermophilus), and the destructive insects which are a scourge to agriculture, become a real plague. We have undoubted fossil evidence that winged insects lived in the Devonian and became numerous in the Carboniferous period. In the egg of these insects a small number of nuclei are formed by the division of the nucleus, and each of these nuclei originates by division the cell-layers of a separate embryo. Brauer, that the Thysanura represent more nearly than any other existing insects the ancestors of the class, has been accepted by the great majority of students. Though feeding largely on worms and insects they ravage gardens and fields, on which account they are detested by the colonists. For instance, the commonest and best-known cases are found in insects where both mimic and model may belong to the same genus, sub-family, family or order, or to different orders. He stamped on the insect. (flying, winged, aquatic) " Watch out for harmful insects. 54. Thus prepared, the specimens are placed on shelves or movable trays, at intervals of about 6 in., in an air-tight cupboard, on the inner side of the door of which, as a special protection against insects, is suspended a muslin bag containing a piece of camphor. Thus he showed that the weevils of granaries, in his time commonly supposed to be bred from wheat, as well as in it, are grubs hatched from eggs deposited by winged insects. Wounds may be artificially grouped, under such heads as the following: Burrows and excavations in bark and wood, due te boring insects, especially beetles. The Mollusca agree in being coelomate with the phyla Vertebrata, Platyhelmia (flat-worms), Echinoderma, Appendiculata (insects, ringed-worms, &c.), and others - in fact, with all the Metazoa except the sponges, corals, polyps, and medusae. Scorpio is here provided with a single or double pair of renal excretory tubes, which have been identified by earlier authors with the Malpighian tubes of the Hexapod and Myriapod insects. In the structure of the digestive system, beetles resemble most other mandibulate insects, the food-canal consisting of gullet, crop, gizzard, mid-gut or stomach, intestine and rectum. It is, for instance, quite likely that certain Herpetomonadine parasites described by Leger (2 9, 34) from various blood-sucking insects are really only stages in the life of a Haemoflagellate. 4. Birds are the natural enemies of many, 14. Of insects there are relatively few kinds; but ants, beetles and mosquitoes abound. In tropical countries ants sometimes make their nests in the hollow thorns of trees or on leaves; species with this habit are believed to make a return to the tree for the shelter that it affords by protecting it from the ravages of other insects, including their own leaf-cutting relations. Now the Pompilidae or mason wasps provision their cells with insects of many different kinds, as well as with spiders; but, of the hundreds of species of these wasps that have been described from different parts of the world, only one is known to use ants for this purpose; and this species is not one that preys upon spiders. Of existing insects 90% belong to the Endopterygota. The insects in the larval or wireworm stage attack the roots of plants, eating them away below the ground. (From Lankester, " Limulus and Arachnid.") Dipterous insects are also very numerous in species, especially in those of sanguinary habits, such as the mosquito, ilium, maroim, carapana, borochudo, &c. In some places these insects constitute a veritable plague, and the infested regions are practically uninhabitable.