Class 3. 



INSECTA. 



473 



the chief part. The tongue, also, cannot be a stranger to this function. The prepara- 

 tory apparatus of the mouth ; the intestinal canal ; the biliary or hepatic vessels, and 

 those which are called salivary, but which are less general ; those free and floating 

 vessels which have received the name of excremental ; the epiploon, or fatty matter ; 

 and probably also the dorsal vessel, — such are the considerations embraced by the 

 digestive system. It is singularly modified, according to the diversity of the food, 

 whence arise a great number of particular types, of which we shall give the description 

 in treating upon the different families. We will only say a few words upon the organs 

 of the mouth [instrumenta cibaria, or trophi, as they have been collectively termed], 

 and the principal divisions of the intestinal canal, commencing with the latter. In those 

 in which it is most complex, such as the carnivorous Beetles, there may be distinguished 

 the pharynx, oesophagus, crop, gizzard, stomach or chylific ventricle, and intestines, 

 which may be divided into the slender intestines, the coecum, and the rectum. In those 

 insects which have the tongue applied upon the anterior or internal surface of the lip, 

 or not disengaged, the pharynx is situated upon this surface : this is its general situ- 

 ation. It is questioned by M. Gaede whether the so-called biliary vessels are in fact 

 secretors, as commonly considered ; but the more recent observations of L. Dufour 

 [published in a valuable series of memoirs in the Annales des Sci. Nat.'\ seem to dis- 

 prove the opinion of M. Gaede. 



Some insects (few in number, and destitute of wings, such as the Myriapoda, or 

 Centipedes) are allied to many of the Crustacea, either in the number of their segments 

 and legs, or in certain points of analogy in the structure of the parts of the mouth ; 

 but all the rest have only six legs, and the body, of which the number of segments never 

 exceeds twelve, is always divided into three principal divisions, — the head, trunk 

 [or thorax], and abdomen. Among the latter individuals, some are destitute of wings, 

 preserving, throughout their whole life, the form which they had at their birth, in- 

 creasing in size only by changing their skins, and which I have named Homotenes, 

 " alike to the end," or the Ametabolia of Leach. They have, in this respect, certain 

 relations with the animals of the preceding classes. 



The other insects with six legs are almost universally winged ; but the last-named 

 organs, and often also the legs, do not appear at first, and are only developed at the 

 close of a series of changes more or less singular, termed metamorphoses, and which 

 we will shortly explain in a following page. The head* bears the antennae, eyes, and 

 mouth. The composition and form of the antennae vary much more than in the 

 Crustacea, and these organs are often much more developed and longer in the males 

 than in the females. 



The eyes are composite or simple. The former, according to the researches of Cuviei, 

 Marcel de Serres, and others, are formed, 1st, of a cornea divided into a multitude of 

 small [hexagonal] parts, and which is more convex according to the carnivorous pro- 

 pensities of the insect, its inner face being spread over with an opaque, scarcely fluid, 

 various-coloured (although generally black, or of a dark violet colour) substance ; 2nd, 

 of a choroid, attached, by its contour and edges, to the cornea, covered with a black 

 varnish, exhibiting a great number of aerial vessels, proceeding from large trunks of 

 the tracheae situated in the head, and of which the branches form around the eye a cir- 



• It:* surface is di\-ided into numerous small regions named clypens 

 {chafifroUf rirftuSf KirbjOi face, forehead, criiwn, and chteiis. The 

 dent)niination of " chaperon '* being equivocal, I have changed it to 

 vpiiitoma: it supports the labnim, or upper lip. [M. StrausK, and some 



other recent anatomists, consider the head as fcrmed of a series of 

 segments soldereil to^^ether, the mnndiiiles, maxilla;, &c., represent 

 ing the limbs attached to each. See also a memoir on the head of in 

 spcta, hr Mr. Newman.] 



