332 1NSKCTA. 



iiea of which is smooth. They are usually three in number, and are 

 disposed in a triangle on the top of the head. In most of the Aptera, 

 and in the larvae of those that are winged, they replace the former, 

 and are frequently united in a group; those of the Arachnides seem to 

 indicate that they are fitted for the purposes of vision. 



The mouth of hexapodous insects is generally composed of six 

 principal parts, four of which are lateral, are disposed in pairs, and 

 move transversely ; the other two, opposed to each other in a contrary 

 direction, occupy the space comprised between the former : one is 

 placed above the superior pair, and the other beneath the inferior. 

 In the triturating insects (broyeurs), or those which feed on solid 

 matters, the four lateral parts perform the office of jaws, the other 

 two being considered as lips ; but, as we have already observed, the 

 two superior jaws have been distinguished by the peculiar appellation 

 of mandibles, the others alone bearing that of maxillae or jaws ; 

 the latter are also furnished with one or two articulated filaments 

 called palpi, a character never exhibited, in this class, by the man- 

 dibles. Their extremity is often terminated by two divisions or lobes, 

 the exterior of which, in the Orthoptera, is called the galea. We 

 have already said that the upper lip was called the labrum. The 

 other, or the labium, properly so styled, is formed of two parts ; the 

 one, inferior and solid, is the mentum or chin ; the other, which is 

 usually provided with two palpi, is the ligula *. 



In the Suctoria, or those that live by the suction of fluid aliament 

 these various organs of manducation present themselves under two 

 kinds of general modifications. In the first, the mandibles and the 

 jaws are replaced by little laminae in the form of setae or lancets, 

 forming, by their union, a sort of sucker, which is received into a 

 sheath, supplying the place of a labium, and is either cylindrical or 

 conical, and articulated in the form of a rostrum, or fleshy or mem- 

 branous, inarticulated, and terminated by two lips constituting a 



* With respect to this, see what is stated in the general remarks which precede 

 the particular exposition of each class. The inferior lip appears to us to be a mere 

 modification of the second jaws of the Crustacea Decapoda, combined with their 

 ligula. The changes gradually effected in these parts in the Crustacea, Archnides, 

 and Myriapoda, seem to authorize this idea. According to this hypothesis, the six 

 thoracic legs are analogous to the foot-jaws, a fact already recognized with regard 

 to the Crustacea of the genus Apus. The five first abdominal segments of the Hex- 

 apoda will then represent those, which, in the Crustacea Decapoda, bear the legs 

 properly so called, or the third and four following pairs of the Amphipoda and Iso- 

 poda. All the observations that have been published on the thorax of Insects, al- 

 though otherwise useful, will necessarily be liable to continual changes, when that 

 part of the body is compared in the three classes of articulated animals provided with 

 articulated feet. In this respect our nomenclature is far from being fixed. 



