224 INSECTA. 



mit air. They all have two antennse and a distinct head. 

 The nervous system of most Insects — the Hexapoda — is gene- 

 rally composed of a brain formed of two opposing ganglions, 

 united at base, giving off eight pairs of nerves and two single 

 ones, and of twelve ganglions(l), all inferior. The two first 

 are situated near the junction of the head with the thorax, 

 and are longitudinally contiguous; the anterior sends nerves 

 to the lower lip and adjacent parts; the second, third and 

 fourth belong to each of the three first segments, or those 

 which form the thorax in the Hexapoda; the remaining gan- 

 glions belong to the abdomen, so that the last or the twelfth 

 corresponds to its seventh ring, and is immediately followed 

 by those which compose the organs of generation; each of 

 these ganglions transmits nerves to the parts of its respective 

 segments. The two last, which are closely approximated, 

 also send some to the terminal annuli of the body. The frontal 

 region exhibits three particular ganglions called frontal by 

 Lyonet, from the first of which arises posteriorly a great 

 nerve with enlargements, the longest of all, that he denomi- 

 nates the recwTcnt. The first ordinary or sub-oesophagean 



of the elytra and that of the wings: they belong to the mesothorax. There are 

 none in the metathorax, unless we consider the two of the first abdominal seg- 

 ment, as supplementary to the thorax, a consideration founded on what occurs in 

 the Diptera and Hymenopterous Insects with a pediculated abdomen, where 

 these two stigmata, with the semi-segment in which they are placed, make part of 

 the thorax. Thus, generally speaking, the hexapoda have eiglit pairs of abdo- 

 minal stigmata, the two last of which, however, are frequently obliterated. 



In Acrydium, Truxalis, and Libellula, each side of the mesothorax presents a 

 stigma, or those which Marcel de Serrcs calls irimaeres. In these latter Insects, 

 as well as in others with naked wings, or without elytra, the two first thoracic stig- 

 mata are placed above, between the prothorax and the mesothorax. With the 

 exception of the Libellulse, the thorax proper offers no other distinct stigmata — I 

 say thorax proper, because, as we have already observed, the two first of the abdo- 

 men, in several, are referable to the posterior extremity of the thorax. The me- 

 tathorax of the Pentatomse, and Scutellerx is provided inferiorly with a pair of 

 stigmata. In the apterous Spectra, there is none in the second segment or meso- 

 thorax; but in the following one, or the metathorax, there are two pairs, one ante- 

 rior, which being situated near the articulation of this segment with the preceding, 

 may be considered as belonging to the latter, and the other smaller, and placed 

 close to that of the first abdominal segment. 



fl) Several of the Lamellicornes in a perfect state form exceptions. 



