Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/165

INSECTS 153 grooves in bark, or earth, in which the eggs are deposited. They are mostly phytophagous, but in some cases carnivorous also. The males are usually very noisy, with special sound-producing organs at the base of the anterior wing. Acri/diidie differ from the last chiefly in the antenna , which are shorter and thick, and in the three-jointed tarsi. The female has no produced ovipositor. They are phytophagous, and the eggs are mostly laid in_ earthen tubes. This family includes (according to modern classification) the true Locusts, notwithstanding the appli cation of the term to the last-mentioned. Sound is produced by friction of the hind thighs against the nervures of the anterior wings. The Orthoptcra have here been treated in a somewhat more de tailed manner than other orders, on account of the bearing of the materials on the classification of insects in general, and the sharply differentiated nature of these materials iu particular. HEMIPTERA. This order consists of insects of very vary ing structure. Primarily there are two great divisions, known as Heteroptera and Homoptera, by some considered distinct orders. The points in which they agree consist especially in an imperfect metamorphosis, and the structure of the mouth, which latter is of a very simple nature, consisting of an elongated articulate tube formed by an extension of the labium into a suctorial organ, concealed in which are bristle-like mandibles and maxilla?, and probably rudiments of maxillary palpi. The tarsi have from one to three joints. In the Heteroptera (or true Bugs) the anterior wings are horizontal, and composed of two distinct parts, the basal portion (or corium) being coriaceous, and the apical portion (or membrane, often unde veloped) being membranous with distinct longitudinal neuration, which latter is only faintly indicated in the coriaceous portion. In repose the membranous portion of one wing overlaps that on the other. The posterior wings are concealed under the anterior, folded, membranous, and with only few nervures. Apterous forms are not uncommon, and sometimes the posterior wings are wanting. This division is again divided into two, Gymnoccrata and Cryptoccrata, in the former of which the antennae are composed of few elongate slender joints, while in the latter the joints are still fewer, short and thick, and ordinarily concealed under the head. Modern writers have erected a multitude of small subdivisions which cannot be enumerated here. The Gymnoccrata are broadly divided into the fol lowing families, viz., Scutcllcridse, Pentatomidw, CorcidiK, Bcrytidx,, Lyg&idie, CapsidcV, T-ingididas, Ecduviidip, Emcsidse, and Saldidw, probably blood-suckers, and members of other families as above given are notorious for a similar habit, amongst which may be par ticularly noticed the genus Acanthia (including the Bed Bug); but the greater part are plant bugs. Most of them are remarkable for emitting a peculiar and often disgusting odour. The Cryptoccrata They prey One genus (Halobates) is remarkable for its pelagic habits, being found on the surface of the ocean very far from land. Many others, such as Notonccta (Water Boatmen or Toe-Biters), Ncpa t llanatra, &c., are very familiar insects. The Homoptera have the wings for the most part deflexed, and the anterior pair not separated into two parts. Often all the wings are membranous, with strong nervures ; in others the anterior pair is coriaceous. The division regarded as a whole is very polymorphic. The true Homoptera have three-jointed tarsi. They may be divided into Cicadidse, (remarkable for the sound-producing organs at the base of the abdomen of the male), Fulgoridae (known as Lantern- Flies, but now known to produce no light ; having the head greatly prolonged in front), Lystridss, Cixiidaz (comprising many little plant- hoppers), Issidfe, Derbidss, Flatidse, Tettigometridte, Membracidx (often of most extraordinary forms), Ccrcopidte (included in which is the Cuckoo-Spit Insect), Ledridte, and Jassidie, all vegetable feeders. The more aberrant Homoptera include well-marked groups. The Fsyllidx are small plant-sucking saltatorial insects with four membranous wings which lie longitudinally deflexed in repose, and with very narrow prothorax, and eight- to ten-jointed antenna} ; they often occasion much damage ; the larva? are frequently covered with a cottony secretion. The Aphidie are the familiar Plant-Lice, the winged forms of which have those organs mem branous, and often extended in repose. The antenna? are five- to seven-jointed. The diversity in form and habits is enormous, and, as is well-known, there are winged and apterous forms in the same species, and parthenogenetic gem-ration of the most extraordinary nature ; and the same species may be both oviparous and viviparous. Most of them void a sweet secretion from abdominal tubes, known as honey-dew, for which they are " milked " by ants. The destruc tion they occasion to plants is very great ; as a now too familiar instance of this, the Phylloxera vastatrix of the grape-vine may be cited. Coccidee (or Scale Insects) have the male two-winged, the female apterous, and living all her life as a fixed "scale" on plants, the organs being of the most rudimentary nature ; the eggs lying under the scale in great numbers ; the tarsi with only one joint" parthenogenesis occurs also in this group ; the male in its earlier stages lives under a special scale. The Cochineal Insect is one of the best known in this group. The little family Alcurodida con sists of minute insects covered with a white waxy secretion. They have four almost nerveless wings in both sexes, two-jointed tarsi the abdomen without secreting tubes, and do not live under scales! In the Hcmiptcra it is now the fashion to include the Anoplura, or true Lice (some also place here the Mallophaya or Bird-Lice), a degraded form of this order, without metamorphosis. Here it is preferred to let them rest in this article, even although some writers do not consider them true insects. The mouth parts certainly have indications of a rostrum, and there are no palpi, and, but for the absence of metamorphosis, there would be little difficulty in fixing the position here as without doubt. All, as is well-known, are epizoic parasites on man and other Mammalia, each speck s being confined to a special host, while attempts have been made to prove that the Head-Louse (Pcdiculus capitis] varies according to the races of men to which it is attached. Perhaps the Crab-Louse (I hthiriua pubia) is regarded with greater disgust than is bestowed upon any other living creature. COLLEMBOLA and THYSANURA. In the introductory notes to this article (p. 141) it is stated that " although it is not difficult to define an insect, speaking broadly, there are certain small groups that do not satisfactorily fall into the class as limited by strongly-defined lines of demarcation." The writer there had especially in view those lice known as Mullophaga and Anoplura, and the two groups indicated in the heading of this section, groups in which metamor phosis, the key of his ideas as to classification, and embody ing an essential requisite in an insect according to common acceptance, is wanting. In the time of Linnaeus, when we were only outside the threshold of knowledge, it may have been sufficient (and perhaps prudent) to include these groups in an order Aptera. But accumulation of knowledge soon dispersed that incongruous order. Such of its elements as could with justice be considered insects have been distributed amongst the various orders. We have not hesitated here to regard the Mallopliaya as degraded Pseiido-Neuroptcra, nor the Anojrtura as equally degraded Hemiptera, notwithstanding that some veterans in entomo logical science may still dispute their position as true insects. There is a breaking-point to elasticity even in ideas of classification, and with regard to the Collcmbola and Thysanura we gladly avail ourselves of the assertion of Lubbock to the effect that they are scarcely within the pale of the true Insecta, notwithstanding the efforts made to locate them in that convenient refuge for the destitute, the Pseudo-Neuroptera. It is certain that the writers in the present work on other classes of Arthropoda will not accept them, and it becomes necessary that they should riot be forgotten. If insects at all, they have in the process of evolution lost the chief attributes of insects, or have never acquired them. Generally both groups are accepted as Thysanura, or as forming two families Podiu-utun, ( = Col- lembola) and Lepismatidx ( = Thysanura). In the Collembola the antenna? arc short, thick, and few-jointed ; the eyes are composed of groups of simple "eye-spots" (much as in the larva; of true insects) varying i:i number ; the mouth organs mandibulate, subject to modifications of a haustellate nature ; the p.ilpi quite rudimentary ; the abdomen consisting of six segments, ami ordinarily provided beneath with a saltatory apparatus (which may, however, be rudimentary) ; no caudal seta 1 . The body is often clothed with prismatic scales, not unlike those of Lcpidoptera. Ordinarily they are minute animals, living in damp places, and sometimes found gregariously. An elongate form is the most general, but Smynthurus and Papirius are short and obese. Lubbock recognizes six families. The true Thysanura arc elongate creatures, not unlike the larvae of Ephemcrulw in form. The antennae are long, slender, and multi- articulate ; the eyes large, compound, ami contiguous (or absent) ; XIII. 20