954 



INSECTA. 



always accompanies that of the trachea. The 

 crura vary much in length in different species. 

 In Neuroptera, Hymenoptera, Lepidoptera, 

 Diptera, and Homoptera they are short and 

 thick, and form with the medulla a thick collar, 

 through which the oesophagus passes as a narrow 

 tube; but in the Gryllida (fig. 410), and 

 more particularly in the Lticanidtf (fig- 413), 

 they are excessively elongated, and they are 

 also of great length in the Timarcha. The 

 medulla oblongata varies much in size ; in some, 

 as in the Lepidoptera, it is as large as one of 

 the lobes of the cerebrum, while in others it is 

 scarcely thicker than the crura. It is always 

 largest where large nerves are required for the 

 parts of the mouth, which in all cases are 

 derived from it. In this respect there is a striking 

 analogy between it and the medulla oblongata 

 of vertebrata. The anterior pair of nerves from 

 this part are given to the labium and lingua, 

 while the two next pairs are given to the man- 

 dibles and maxilla. In the distribution of these 

 nerves there is great similitude to that of the 

 fifth pair in the higher animals. In the larva 

 state these nerves are always distinct from each 

 other, but in the perfect they are often united 

 at their base into one trunk. This is the case 

 in the Timarcha and Gryllida. The anterior 

 pair is the largest in mandibulated insects, 

 and supplies the powerful mandibles, while 

 the posterior pair is given to the maxilla. The 

 union of these nerves at their base is interesting 

 from the circumstance that during manducation 

 a consentaneous movement of these parts is 

 required, since, while the mandibles are em- 

 ployed in chewing, the maxillae are also em- 

 ployed in turning and assisting to pass the food 

 into the pharynx. In the Sphinx ligustri, and 

 other Lepidoptera, the chief portion of the man- 

 dibular nerve has disappeared in the perfect 

 state, in consequence of the atrophy which has 

 taken place in the mandibles during the trans- 

 formations ; but one branch of the nerve which 

 exists in the larva state appears to have become 

 approximated to the maxillary nerve, which is 

 now greatly elongated and given to the pro- 

 boscis, the representative of the maxillae of 

 the larva. The branch that appears to have 

 belonged to the mandibular nerve is extended 

 along the concave or inner side of each half of 

 the proboscis, where the sense of taste may 

 justly be suspected to reside, and is traceable 

 very nearly to the extremity of the organ, where 

 the papillae we formerly noticed are situated, 

 and in the direction of which this nerve is 

 extended. From this we believe it to be 

 analogous in function to the gustatory portion 

 of the fifth nerve in vertebrata. In Lucanus 

 cervus the mandibular nerve is of great length, 

 and is so extensively developed as to afford 

 almost a proof of the elongation of nerves 

 during the metamorphoses of the insect. We 

 have traced this nerve from its origin (Jig. 

 413, c) into the base of the mandible, which it 

 enters a little external to the insertion of the 

 flexor muscles, where it is divided into three 

 trunks, the inner one of which we have traced 

 very nearly as far as the apex of the mandible. 

 The other two are situated more externally. 



Nervous system of Lucanus cervus. 



A, the brain ; B, optic nerves ; C, sympathetic ; 

 D, antennal nerves; a, ganglion of the vagus 

 nerve ; b, the nerve ; i, its division on the oeso- 

 phagus ; d, nerve to the first pair of legs ; /, 

 nerve to the wings, giving off at its base a small 

 nerve to the elytra ; g, nerve to second pair of 

 legs ; k, to third pair ; I, abdominal cord and 

 ganglia. 



