INTERNAL ANATOMY OF INSECTS. 11 
moth, these in one respect differ remarkably from the 
chords that connect them; in the latter the air-vessels or 
bronchize only cover the outside of the tunic, while in the 
former they enter the substance of the ganglion, which 
is quite filled with their delicateand numberless branches ?. 
Every ganglion may be regarded in some degree as a cen- 
tre of vitality or little brain, and in many cases, as well 
as the brain, they are formed of two lobes‘. I shall now 
consider them more 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*; in 
others, as in the louse, the water-scorpion, and the grub 
of the rhinoceros-beetle (Oryctes nasicornis), they are 
confined to the ¢runk, their functions in the abdomen be- 
ing supplied by numerous radiating nerves*; in others 
again, as in the scorpion, they are all abdominal. The 
ganglions vary also in their situation with respect to each 
other. Thus in some, as in the larva of the Chamzeleon- 
fly (Stratyomis Chameleon), they are so near as to appear 
like a string of beads‘; in that of the ant-lion (Myrme- 
leon) the two ganglions of the trunk are separated by an 
interval from those of the abdomen, which are so conti- 
2 Lyonnet Anat. 100. b N. Dict. d’ Hist. Nat. xxii, 522—, 
© Lyonnet whi supr. t. ix. f. 1—4. 
4 Cuy. Anat. Comp. ii. 339. 343. ® Prate XXI. Fie. 7. 
£ Swamm. whi supr. t. xl. f. 5. Cuvier (ii. 332.) accuses Swam- 
merdam of representing the spinal marrow in this grub as producing 
nerves only on one side; whereas he expressly states (ii. 50. b.) that a 
considerable number spring on each side from the eleven ganglions, 
but that to avoid confusion he had omitted some. 
