612 



NERVOUS SYSTEM. (COMPARATIVE ANATOMY.) 



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approximated, though by a lens the fissure or 

 mark of separation may in some be perceived. 

 The abdominal ganglia are of a lengthened 

 ovoid form ; and when viewed through a lens, 

 have a dense opaque white appearance ; two 

 in particular appear encased as it were in a 

 neurilemma, and have a distinctly bilobate ap- 

 pearance ; in others there appears quite a 

 nucleus of opaque nervous matter (8 & 9) ; from 

 each of them are given off three lateral pairs of 

 nerves, some of which pass to supply the 

 viscera, while others pass roucd the body of 

 the larva to near the dorsal vessel, thus forming 

 a nervous ring, open superiorly, which being 

 repeated in each segment, and the whole con- 

 nected by commissures, forms a continuous 

 series at once recognised as a column of pri- 

 mary nervous rings, the type of the nervous 

 system of the articulata; the eleventh and 

 twelfth ganglia are closely joined to each other, 

 and from the latter are given off two radiating 

 pairs of nerves, passing to the caudal extremity 

 of the larva. There is also a minute nerve 

 (Jig. 348, f), which I have traced in this larva 

 passing off at the angle of separation between 

 the divided longitudinal cords connecting the 

 second and third, and the third and fourth 

 abdominal ganglia, and which, midway be- 

 tween these ganglia, divided into a right and 

 left transverse filament (g, g), each of which 

 had connexion with the lateral nerves arising 

 from the ganglia themselves. Some have con- 

 sidered these nerves as sympathetic, others 

 as motor, but from their principal branches 

 going to supply the tracheae, I consider, with 

 Mr. Newport, that they must be respiratory 

 nerves. 



I have examined the nervous cord in the 

 larva of Pontia brassica, Cossus ligniperda, 

 two species of Arctia, and have found the dis- 

 position of the ganglia, &c. to be the same ; 

 as the insect, however, advances towards ma- 

 turity, considerable and important changes take 

 place in the nervous system. Heroldt has 

 described and figured them in the Pontia bras- 

 sica,* and Mr. Newport has investigated them 

 with the minutest accuracy in the Sphinx li- 

 gustri.f It appears that during the pupa state 

 a contraction of the nervous columns takes 

 place, the ganglia (more particularly the se- 

 cond, third, fourth, and fifth) become approxi- 

 mated ; the distance between the cerebral gan- 

 glion and the first sub-cesophageal ganglion 

 becomes much less, and the cesophageal ring 

 becomes much smaller; this is preparatory to 

 the subsequent concentration and junction 

 which we find in the perfect insect. When 

 this latter phenomenon takes place, the ganglia 

 just mentioned become consolidated together, 

 and the oral nervous ring is scarcely percep- 

 tible : this is the case in the perfect state of 

 Mormo maura (fig. 349), where also the ab- 

 dominal ganglia are small (c f), and (owing to 

 the disappearance of two of the thoracic ganglia) 

 are situated at some distance from these latter, 

 which are of large size (b b\ and the nervous 



* Entwickelungsgpschichte des Schmetterlings. 

 f Phil. Trans, for 1832 and 1834. 



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/V. 343 



