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Show 226 INSECTA. apparatus, intestinal canal, biliary vessels, also called hepati vessels, those styled salivary, but whic.h .a re less general ' fre: and floating vessels called excrementitiOus, the epiploon or corps graisseux, and probably of the dorsal vessel. Thissys· tern is singularly modified accot'ding to the difference of the aliment, or forms a great number of particular types, of which we shall speak when t1·eating of families. We will merely say a word with respect to the buccal apparatus and the prin. cipal divisions of the intestinal canal, beginning with the lat. ter. In those where it is the most complicated, as in the carnivorous Coleoptera, we observe a pharynx, msophagus, crop, gizzard, stomach or chylific ventricle, and intestines which are divided into the small intestines, great intestine or crecum, and the rectum. In those Insects where the tongue, properly so called, is laid on the anterior or internal face of the lip, or is not free, the pharynx is situated on that same face, and this is most commonly the case( 1). We will also add, that a naturalist who first furnished us with correct ob. servations on the respiratory organs of the Mygales, M. Gaede, professor of natural history at Liege, does not consider the biliary vessels as secreting organs-this opinion, however, does not appear to be sufficiently well founded, and the ob. servations of M. Leon Dufour(2) even seem to destroy it. Some few, and always apterous Insects, such as the Myria· poda, approximate to several of the Crustacea, either in the number of the annuli of their body and in their legs, or in some points of analogy in the conformation of the parts of the mouth; but all the others never have more than six legs, and their body, the number of whose segments never extends beyond twelve, is always divided into three principal parts, the head, trun~ and abdomen. Among the latter Insects, some are found (1) See what we have stated respecting the ligula, ill our general remarks on the three classes. (2.) This l~tter naturalist, whom I shall have ft·equent occasion to mention, hu pubhshed, w1th the most minute detail, every thing relative to the digestive •Y" tern of ~nsects, in a set·ies of admirable Memoirs, which have enriched the Annalcs des S~tences Naturelles. A well arranged resume of the whole by M. Victor Audoum may be found in the Diet. Class. d'Hist. Nat., article bncus. J NSECTA. 227 without wings, that always preserve their natal form, and merely increas~ in size and change their skin(l ). In this respect they bear some analogy to th~ animals of the ]lreceding cla~es. Nearly all the remaining Hcxapoda have wings; but these organs, and even frequently the feet, do not make their appearance at first, but are only developed afttr a series of changes, more or less remarkable, styled metamorphoses, of which we shall soon have to speak. The head(~) bears the antennm, eyes, and mouth. The composition and form of the antennre are much more various than in the Crustacea, and are frequently more developed or longer in the males than in the females. The eyes are either compound or simple; the fint, according to the baron Cuvier, Marcel de Serres and others, are formed: 1, of a cornea, divided into numerous little facets, which is so much the more convex, as the insect is more carnivorous; its internal surface is covered with an opaque, and variously coloured, but slightly fluid substance, usua11y, however, of a black or deep violet hue ; 2, of a choroides, fixed by its contour and edges to the cornea, covered with a blac~ varnish, exhibiting numerous air vessels, arising f1·om tolerably large trunks of trachere in the head, whose branches form a circular traohea round the eye: it is frequently wanting, however, as weB as the choroides, in various nocturnal insects; 3, of nerves arising from a large trunk, proceeding directly from the brain, which then opens, forming a reversed cone, the base of which is next to the eye, and each of whose rays or threads traversing the choroides and lining matter of the cornea, terminates in one of its facets ; there is no crystalline nor vitreous humour. Several, besides these compound eyes, have simple ones, the cornea of which is smooth. They are usually three in (1) My Ilomotenes (similar to the end) or the .!lmetobolia of Leach. (2) Its surface is divided into several little regions or arere called the clypem (nose of Kirby), the face, the front, the vc1·tex or summit, and the clteeks. The term clypeus being equivocal, I have substituted for it that of epistuma or overmouth. It gives insertion to the labrum or uppet· lip. |
