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Show 240 INSECTA. the others, as well as the segments on which they depend, are developed by age. · But few vegetable substances are protected from the vora-city of Insects; and a.S those which are necessary or useful to Man are not spared by them more than others, they become very injurious, particularly during seasons which favour their multiplication. Their destruct~on gr~atly depends upon our vigilance and knowledge of their _habits. Some of them are omnivorous-such are the Termites, Ants, &c., whose ravages are but too well known. Several of those which are carnivorous, and all the species which feed on dead animal and excrementitious matters, are a benefit conferred on us by the Author of Nature, and somewhat compensate for the inconvenience and injury we experience from the others. Some are employed in medicine, the arts, and our domestic economy. They have numerous enemies: Fishes destroy many of the aquatic species; Birds, Bats, Lizards, &c., deliver us from a part of those which inhabit the air or earth. Most of them endeavour to escape by flight or running from the dangers that surround them, but some have recourse to stratagem or arms. Having undergone their ultimate transformation, and being possessed of all their faculties, they hasten to propagate their species :-this aim once accomplished, they soon cease to exist. Thus, each of the three finer seasons of the year pro· duces species peculiar to it. The females and males of those which live in societies, however, enjoy a longer term of life. Individuals hatched in autumn shelter themselves from the rigours of winter, and reappear in spring. The species, like those of plants, are circumscribed within geographical limits. Those of the western continent for in· stance, a very few, and all from the north, excepted, are strictly peculiar to it ; such also is the case with several ge· nera. The eastern continent, in turn, possesses others which are unknown in the western. The Insects of the south of Europe and north of Africa, and of the western and southern countries of Asia, have a strong mutual resemblance. The INSECTA. 241 me may he said of those which inhabit the Moluccas, and 5~ore eastern islands, those of the Southern Ocean included. ;everal northern species are found in the mountains of southern countries. Those of Africa differ greatly from the opposite portions of America. The Insects of Southern Asia, from the Indies on the Sind eastward, to the confines of China, are very much alike. The intertropical regions, covered with immense and well watered forests, are the richest in Insects of any on the globe; Brazil and Guiana are particularly so. All general systems or methods relative to Insects are reduced e sentially to three. Swammerdam based his on their metamorphoses; that of Linn reus was founded on the presence or abscnceofwings, their number, consistence, superposition, the nature of their surface, and on the deficiency or presence of a sting. Fabricius had recourse to the parts of the mouth alone. In all these arrangements the Crustacea and Arachnides are placed among the Insects, and in that of Linnmus, the one generally adopted, they are even the last. Brisson, however, had separated them, and his class of the Crustacea which he places before that of Insects, comprises ali of those animals which have more than six feet, or the lnsectes .!lpirojJodes of M. Savigny. Although this order is more natural than that ofLinnreus, it was not followed; and it is only in modern times, that anatomical observations and their rigorously exact application have brought us to the natural method(!). I divide this class into twelve orders: the three first of which; composed of apterous Insects, undergoing no essential change of form or habits, merely subject to simple changes of tegument, or to a kind of a metamorphosis, which increases the number of legs, and that of the annuli of the body ; correspond to the order of the .flrachnides antennistes of Lamarck. The organ of sight in these animals is usually a mere ( rnm·e or Jess considerable) assemblage of simple eyes resembling granules. The (I) Cuv., Tabl. Elem. de l'Hist. Nat. des Anim., and Lel(ons d' Anat. Compar.; Lamarck, Syst. des Anim. sans Verteb.; Latr., Precis des Caract. Gener. des Insect., and Gen. Crust. et Insect. For more minute details, see also the excellent elementary work of Kirby and Spence. Vot. III .-2 F |
