228 INSECTA. 



number, and are disposed in a triangle on the top of the head. 

 In most of the Aptera and in the larva; 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 be- 

 tween the former: one is placed above the superior pair, and 

 the other beneath the inferior. In the triturating insects (bro- 

 yeurs), or those which feed on solid matters, the four lateral 

 parts perform the ofHce of jaws, the other two being consi- 

 dered as lips; but, as we have already observed, the two supe- 

 rior 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 fila- 

 ments caWed palpi, a character never exhibited, in this class, 

 by the mandibles. Their extremity is often terminated by 

 two divisions or lobes, the exterior of which, in the Orthop- 

 tera, is called the galea. We have already said that the upper 

 lip was called the labrum. The other, or the labium pro- 

 perly 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{\). 



(1) with respect to this, see what is stated in the general remarks which pre- 

 cede 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, 

 Arachnides, and Myriapoda, seem to authorize this idea. According to this hy- 

 pothesis, the six thoracic legs are analogous to the foot-jaws, a fact already recog- 

 nized with regard to the Crustacea of the genus ^pus. The five first abdominal 

 segments of the Hexapoda will then represent those, which, in the Crustacea De- 

 capoda, bear the legs properly so called, or the third and four following pairs of 

 the Amphipoda and Isopoda. All the observations that have been published on 

 the thorax of Insects, although otherwise useful, will necessaril}'^ be liable to con- 

 tinual changes, when that part of the body is compared in the three classes of 

 articulated animals provided with articulated feet. In.this respect our nomencla- 

 ture is far from being fixed. 



