134- INTERNAL ANATOMY OF INSECTS. 
Treviranus calls it a sa//i>a-vessel * — since in the Mi/gale 
avicularia and other spiders, the effect of the bite is said 
to be so venomous as to occasion considerable inflamma- 
tion, and sometimes death b . 
v. Scent-secretors (Osmateria). Amongst other means 
with which insects are gifted for the annoyance of their 
foes and pursuers, are the powerful scents which many of 
them emit when alarmed and in danger. Concerning 
the internal organs by which these effluvia are secreted 
we possess but little information, but more notice has 
been taken of the external ones by which they are emit- 
ted. We may conclude in general, that the secretory 
organs are membranous sacs or vesicles, perhaps termi- 
nating in longer or shorter blind filiform vessels, some- 
times secreting a fetid fluid, and at others a fetid gaseous 
effluvium. The lulidce, at least lulus and Porcellio , cover 
themselves when alarmed, with a Jluid of this kind, or 
emit one, for this faculty is not peculiar to the species 
noticed by Savi. I observed early in the year, when I 
handled Iidus terrestris, that it was covered with a slimy 
secretion, of a powerful scent, which stained my fingers 
of an orange colour. The spiraculiform pores that mark 
the sides of the animal are the outlets by which this fluid 
is emitted, and not spiracles as has been supposed : each 
of these orifices, as we learn from Savi, terminates in- 
ternally in a black vesicle, which is the reservoir of the 
fluid d . The most remarkable insect for its powers of 
annoyance in this way, is one on that account called the 
bombardier {Brachmus crepitans), which can fire nume- 
a Arachnid. 31. t. W.f. 21. p. 9. b N. Diet. cVHist. Nat. xxii. 
1 14. 117. comp. Vol. I. p. 127- c Ibid, xxviii. 6. 
d Osservazioni, &c. 13 — . 
