INSECTA. 



963 



Immediately 

 after chanyitig 



Half-an-kour * a pupa. 



before 



clianging. 



Fvll-groycn 

 lana. 



(Newport, Ph. Trans.) 

 there is great excitement throughout the body of 

 the insect. About half-an-hour (Jig. 419, 2) 

 before this occurs the alary nerves and the 

 cerebral, second, third, fourth, and fifth ganglia 

 are slightly enlarged, and the medulla or first 

 sub-cesophageal ganglion very considerably. The 

 cords that extend between them diverge much 

 from each other, while those between the fiftri, 

 sixth, and seventh ganglia, are disposed in a more 

 zig-zag direction than in other parts of the body. 



Immediately after the insect has entered the 

 pupa state (3), all the ganglia are brought 

 closer together in consequence of the cords 

 being disposed more irregularly than at any 

 other period, which has been occasioned by the 

 shortening that has taken place in every seg- 

 ment, by which the cords are rendered too long 

 to lie in a direct line. The cords which con- 

 nect the first five ganglia are slightly increased 

 in size, and the fourth and fifth and their inter- 

 vening cords, in which the first great changes 

 commence, are often nearer together, and have 

 become more united at this period of the trans- 

 formation, in some specimens, than in others 

 at five or six hours later. This is in accord- 

 ance with what we have observed in the Sphinx 

 ligustri, in which the precise period when the 

 union of ganglia takes place cannot positively 

 be ascertained in consequence of its differing 

 in different specimens according to the vigour 

 of the insect, or to the temperature of the 

 season at the time of changing. 



One hour after (Jig. 421, 4) the transform- 



Onekour after Twefce Itavrs. Eighteen hour*. 



changing. 



ation the cerebral ganglia are found to be more 

 closely united, the antennal nerves more dis- 

 tinct, and the optic nerves more enlarged at 

 their base. The fourth and fifth ganglia are 

 approaching each other, and the cords are en- 

 larged at their connexion with the latter, the 

 anterior part of which has become less dis- 

 tinct, and seems about to coalesce with them. 

 The distance between the remaining ganglia is 

 also reduced, and the investing membrane, or 

 exterior surface of the cord exhibits a corrugated 

 appearance as if in the act of becoming 

 shortened. We have seen in the account pre- 

 viously given of the nervous system in the 

 larva of the Sphinx, that besides the longi- 

 tudinal cords and ganglia, and the nerves dis- 

 tributed from them, there are also the trans- 

 verse nerves. There are like nerves in Papilio 

 wtiw, and which are distributed to the same 

 parts as in the Sphinx. They commence be- 

 hind the first sub-cesophageal ganglion or me- 

 dulla, where the first of them pass directly out- 

 wards in the course of the tracheae that come 

 from the first spiracle, and distribute and give 

 some branches to the surface of the medulla 

 and its nerves, and some also to the second 

 ganglion (d), while the main branch passes 

 along in the direction of the muscles of the 

 back part of the head. Behind the second 

 ganglion branches of tracheal vessels, and 

 also a nerve from the transverse plexus, are given 

 to the great alary nerve ( / ) that arises in this 

 insect singly from the cord between the second 

 and third ganglion, and not, as in the Sphinx, 

 one portion from the cord and another from the 

 ganglion posterior to it. From the cord be- 

 tween the third and fourth ganglion arises the 

 second alary nerve (i), which like the preceding 

 arises singly from the cord, but receives also a 



1832. 



3 R 2 



