548 THE SENSORIAL FUNCTIONS. 



This system in the larva (Fig. 442) has the 

 same simple form as in the Annelida, or in the 



phalic, or cerebral ganglion (17) is situated above the oesophagus 

 and dorsal vessel, and communicates by two nervous cords with 

 the first of the series, or sub-cesophageal ganglion (1), which is, in 

 every stage of the insect, contained within the head, and distri- 

 butes nerves to the parts about the mouth. The next ganglion 

 (2) becomes obliterated at a late period of the change from the 

 pupa to the imago state : the third (3) remains, but the two 

 next (4, 5) coalesce to form, in the imago, the large thoracic 

 ganglion ; while the two which follow (6 and 7), become wholly 

 obliterated before the insect attains the imago state, the interven- 

 ing cords becoming shorter, and being, with the nerves they send 

 out, carried forwards. The last four (8, 9, 10, 11) of the abdo- 

 minal ganglia remain, with but little alteration, in all the stages 

 of metamorphosis : in the larva, they supply nerves to the false 

 feet. The nerves (12, 13) which supply the wings of the imago, 

 are very small in the larva; and they arise by two roots, one derived 

 from the cord, and one from the ganglion. The nerves sent to 

 the three pair of anterior, or true legs, are marked 14, 15, 16. 



The nervous system of the larva is exhibited in Fig. 442, that 

 of the pupa in Fig. 443, and that of the imago in Fig. 444. It 

 will be seen that in the pupa the abdominal ganglia are but little 

 changed ; but those situated more forward (6, 7) are brought 

 closer together by the shortening of the intervening cord, prepa- 

 ratory to their final obliteration in the imago ; a change which 

 those in front of them (4, 5) have already undergone. The pro- 

 gressive developement of the optic (18) and antennal (19) nerves 

 may also be traced. Mr. Newport has also traced a set of nerves 

 (20) which arise from distinct roots, and which he found to be 

 constantly distributed to the organs of respiration. 



A detailed account of the anatomy of the nervous system of the 

 Sphinx ligustri, and of the changes it undergoes up to a certain 

 period, is given by Mr. Newport in a paper in the Phil. Trans, for 

 1832, p. 383. He has since completed the inquiry to the last 

 transformation of this and other insects, and has lately presented 

 to the Royal Society an account of his researches. 



