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 nasicornis, and the cheese-mag- 

 got, there are no internodes, the spinal marrow being 

 formed of knots separated only by slight or deep con- 

 strictions . 



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 

 bronchiaa 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 6 . 

 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 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 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. sujir. 348. b Treviranus Arachnid, t. v./. 45. 



c PLATE XXI. FIG. 7. 8. Swamra. Bibl. Nat. t. xliii./. 7. 

 d PLATE XXI. FIG. 7. 8. c. e Lyonet Anat. 100. 



f N. Diet. d'Hist. Nat. xxii. 522. 

 K Lyonet ubi supr. t. ix./. 1 4. 

 h Cuv, Anal. Camp* ii. 339. 313. 



