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 in 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) and Acrida 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 Brassiccc) the 
Jive first are double, and the six last single f ; in that of the 
great goat-moth {Cossus lignipcrda) the three [first only are 
double, but the others terminate in a fork s ; in the cock- 
roaches (Blatta) the four fost, in Hydrophilus piccus 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 Hypogynpia dispar; all the internodes are 
a Arachnid, t. v.f. 45. b Swamm. ubi supr. t. xliii./. 7- 
e Ibid. 112. a. " Cuv. Anat. Comp. ii. 337. 343—. 
c Ibid. 33G. f Herolcl Schmetterl. t. ii./. 1. 
e Lyonet Anat. 98. 
h Cuv. ubi supr. 342. Gaede N. Act. Acad. Cos. XL. ii. 323. XTuv. 
Ibid. 351. 
