4 CLASS INSECTA. 



They all have two antennae, and a head distinct. The 

 nervous system of the majority of insects (the hexapodes) is 

 generally composed of a brain formed of two opposite gan- 

 glia, united at their bases, giving but eight pairs of nerves, 

 and two solitary nerves, and twelve ganglia,* all inferior. 

 The first two are situated near the junction of the head with 

 the thorax, and longitudinally contiguous ; the anterior gives 

 out nerves to the under lip, and to the parts adjacent. The 

 second and the two following are proper to each of the first 

 three segments, or those which in the hexapode insects com- 

 pose the thorax, Tlie other ganglia belong to the abdomen, 

 so that the last, or twelfth, corresponds to its seventh ring, 

 followed immediately by those which compose the several 

 organs. Each of these ganglia give out nerves to the parts 

 of their respective segments. The two last, very closely ap- 

 proaching each other, also give out nerves to the last rings of 

 the body. The frontal region has three particular ganglia, 

 designated by Lyonet under the name of frontals, and the 

 first of which produces, posteriorly, a thick nerve with 

 swellings : this is the longest of all the nerves, and he names 

 it recurrent. The first ordinary ganglion, or the suh-oesopha- 



M. Marcel de Serres names tremaeres. In these last mentioned insects 

 as well as in the others with naked wings, or without elytra, the first 

 two thoracic stigmata are placed above, between the prothorax and meso- 

 thorax. With the exception of the libellulae, the thorax proper exhibits 

 no distinct stigmata. I say the thorax proper, because, as we have re- 

 marked above, the two first of the abdomen are referred by many to the pos- 

 terior extremity of the thorax. The metathorax of the pentatomata and 

 Scutellaria exhibits one pair of stigmata underneath. In the aptera, 

 the second segment, or mesothorax, has none ; but the following segment, 

 or metathorax, has two pairs, one anterior, and which, being situated near 

 the articulation of this segment with the preceding, may be deemed to 

 belong to this last, and the other smaller, and placed very near that of 

 the first abdominal segment. 

 * Divers lamellicorneous coleoptera in the perfect stateform an exception. 



