INTERNAL ANATOMY OF INSECTS. 13.'> 
rous volleys of stinking vapour at its assailants before its 
ammunition is exhausted a . M. Dufour has given a very 
particular account of the organ that secretes this vapour; 
— it consists of a double apparatus, one on each side, in 
the cavity of the abdomen, both formed of two distinct 
vessels. Thejirst, which is the innermost, presents it- 
self under two different aspects, according as it is con- 
tracted or dilated : in the former case it is a whitish, 
irregularly rounded, soft body, apparently glandular, 
placed under the last abdominal segments ; communica- 
ting at one end with the reservoir, and terminating con- 
stantly at the other in a very long and slender filament : 
in the second case, or when it is dilated, it resembles an 
oblong, membranous, diaphanous sac, filled with air, 
then occupying the whole length of the abdomen, and 
appearing free except where it communicates with the 
reservoir. The second vessel or reservoir is a small, 
spherical, brown or reddish body, constant in its form, 
internally hollow, placed under the last dorsal segment, 
precisely above the rectum, and opening by a small pore 
into the anus b : so that the tail of this little beetle may 
be regarded as a battery mounted with two pieces of 
cannon, which our alert bombardier fires alternately 
without intermission till all his ammunition is expended. 
The ground-beetles (Eutrech'ma) in general have a pair 
of these anal scent-secretors, which discharge an acrid 
and caustic fluid, and sometimes a volatile one c . The 
external organ of the scent-secretors in Gyrimts consists 
of two minute hairy cylindrical retractile tubes, of a red 
colour d . Numerous insects of other tribes and genera 
3 Vol. II. p. 243—. N. Diet. d'Hist. Nat. iv. 308. b Ibid. iv. 300. 
c Ibid. v. 252. d Dc Gcer iv. 358. /. xiii./. 9. m. 
