NERVOUS SYSTEM OF INSECTS. 385 



* 



go states, wholly detached from the body, and of their na- 

 tural size, in Figures 442,, 443, and 444.* 



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

 form as in the Annelida, or in the Talitrus, for it consists of 



* These figures were drawn by Mr. Newport, from original preparations 

 made by himself. The same numbers in each refer to the same parts; so 

 that by comparing the figures with one another, a judgment may be formed 

 of the changes of size and situation which occur in the progress of the prin- 

 cipal transformations of the insect. Numbers 1 to 11 indicate the series of 

 ganglia which are situated along the under side of the body, and beneath 

 the alimentary canal. Of these the first five are the thoracic, and the last 

 six the abdominal ganglia; while the cephalic, or cerebral ganglion (17) is 

 situated above the oesophagus and dorsal vessel, and communicates by two 

 nervous chords 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 ima- 

 go, the large thoracic ganglion; while the two which follow (6 and 7,) be- 

 come wholly obliterated before the insect attains the imago stale, the inter- 

 vening cords becoming shorter, and being, with the nerves they send out, 

 carried forwards. The last four (8, 9, 10, 11) of the abdominal ganglia re- 

 main, 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 sup- 

 ply the wings of the imago, are veiy 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 pairs 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 inter- 

 vening cord, preparatory to their final obliteration in the imago; a change 

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

 gressive development 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 endergoes 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. 



VOL. II. 49 



