INTERNAL ANATOMY OF INSECTS. 11 
single, except the second, the chords of which at first are 
separate, and afterwards united a ; and, to name no more, 
in Clubiona atrox there is only one internode, which is 
single, with a longitudinal furrow b . In some, as in the 
louse, the grub of Oryctes Tiasicornis, and the cheese-mag- 
got, there are no internodes, the spinal marrow being 
formed of knots separated only by slight or deep con- 
strictions c . 
I must next say something of the ganglions d . Lyonet 
has observed that, in the caterpillar of the great goat- 
moth, these in one respect differ remarkably from the 
chords that connect them ; in the latter the air-vessels or 
bronchiae only cover the outside of the tunic, while in the 
former they enter the substance of the ganglion, which is 
quite filled with their delicate and numberless branches e . 
Every ganglion may be regarded in some degree as a cen- 
tre of vitality or little brain f , and in many cases, as well 
as the brain, they are formed of two lobes g . I shall now 
consider them moi'e particularly as to their station, num- 
ber, and shape. 
1. With regard to the first head, their station, they 
are most commonly divided between the trunk and ab- 
domen ; but in some cases, as in Hydrophilus piceus and 
Acrida viridissima, the Jirst ganglion is in the head h ; 
in others, as in the louse, the water-scorpion, and the 
grub of the rhinoceros-beetle, they are confined to the 
trunk, their functions in the abdomen being supplied 
a Cuv. ubi. supr. 348. b TYeviranus Arachnid, t. \.f. 45. 
c Plate XXI. Fig. 7- 8. Swamm. Bibl. Nat. t. xliii./. 7. 
d Plate XXI. Fig. 7. 8. c. e Lyonet Anat. 100. 
f N. Diet. d'Hist. Nat. xxii. 522—. 
6 Lyonet ubi supr. t. ix./. 1 — 4. 
" Cuv. Anat. Cemp. ii. 331). 343. 
