10 INTERNAL ANATOMY OF INSECTS. 



that animal, would be below the intestines ; from the 

 figures of Treviranus it should seem that the spiders, at 

 least Clubiona atrox^ are similarly circumstanced a ; in 

 the cheese-maggot, which turns to a two- winged fly 

 ( Tyrophaga Casei), the chord is also single, but it has 

 a small orifice through which the gullet passes b . At 

 the union of the chords i# other cases below that organ, 

 a knot or ganglion is usually formed, and an alternate 

 succession of internodes and ganglions commonly fol- 

 lows to the end. The internodes also may generally be 

 stated to consist of a double chord, though in many 

 cases the two chords unite and become one, or are distin- 

 guished only by a longitudinal furrow, and even where 

 they are really distinct and separable, in the body of the 

 insect they lie close together c . In the rhinoceros beetle 

 (Oryctes nasicornis) andAcrida viridissima &c. all the in- 

 ternodes consist of a double chord d ; but in many other 

 insects numerous variations in this respect occur. Thus 

 in the stag-beetle the last internode is single e ; in the ca- 

 terpillar of the cabbage butterfly (Pontia Brassier) the 

 jive first are double, and the six last single f ; in that of the 

 great goat-moth (Cossus ligniperda] the threejirst only[are 

 double, but the others terminate in a fork s in the cock- 

 roaches (Blalta) thefotirjirst) in Hydrophilus piceus the 

 three Jirst, and in Eristalis tenax the two jirst only are 

 double, the rest being all single h . A singular variation 

 takes place in Hypogymna dispar; all the internodes are 



a Arachnid, t. v.f. 45. b Swamm. ubi supr. t. xliii./. 7. 



c Ibid. 1 12. a. ' d Cuv. Anat. Comp. ii. 337. 343. 



c Ibid. 336. f Ilerold Schmetterl. t. ii./. 1. 



g Lyonet Anat. 08. 



h Cuv. ubi supr. 343. Gaede N. Act. Acad. Cas. XL. ii. 323. Cuv. 

 Ibid. 351. 



