378 



. ZOOLOGY. 



proach each other, and become confused into a nervou- 

 The cephalic ganglions ;nv large, and give origin to theiirrvrs 

 of the eves and antennae, &c. The first pair of ganglions 

 hehind the gullet give off the nerves of the mouth, and the 

 longitudinal filaments connecting them with the cephalic 

 ganglions from the nervous collar surrounding the gullet. 

 Finally, the brain gives off on each side a 

 nerve, which, ascending on the stomach and 

 uniting with that of the opposite side, consti- 

 tutes a median nerve, situated above the di- 

 gestive canal, and having in its course t\\<> 

 ganglions. The three pairs of ganglions fol- 

 lowing behind the gullet belong to the three 

 rings of the thorax, and give off the nerve of the 

 limbs and wings; generally speaking, they 

 are very near each other, and much larger than 

 the following pairs, which belong to the ab- 

 domen. 



521. Insects vary much in their mode 

 of nourishment, some living on the juice of 

 plants, whilst others feed on solid aliments, 

 and are either carnivorous or phytophagous ; and 

 these differences correspond to a remarkable 

 modification in the structure of the mouth. 

 In the grinding insects, such as the scarabei, 

 the may-bug, the blatta (Fig. 355), the grass- 

 hoppers, the opening of the mouth is furnished 

 anteriorly with a median piece called labium, 

 or upper lip (a, Fig. 356), and present- 

 each side a kind of large moveable tooth, very 

 Fig. 354. hard, and called mandible (b, Fig. 356), which 

 serves to divide the food. Immediately behind 

 these are the more complex jaws (c, Fig. 356). Each of these last 

 organs offers besides a plate or a cylinder, more or less hard, 

 armed with small teeth or hairs, and carries on its outer >ide 

 one or two small stalks composed of several joints, called max- 

 illary palpi. Finally, behind the jaws is a second pair of ap- 

 pendages, whose base is supported by a median horny pieee, 

 called the chin (d) ; these appendages constitute the languette 

 or little tongue. They are applied against the jaws as those 

 are themselves applied against the mandibles ; there exists lie- 

 sides a pair of articulated and moveable filaments called labial 

 palpi, because the name of lower lip is usually given to the chin 



