A454 MODERN CLASSIFICATION OF INSECTS. 
previously passed over or sucked its juices. Some species, however, 
are destitute of this means of defence, and these are chiefly found 
amongst the predaceous species, with a short curved rostrum. ‘The 
exhalation of this scent is not, however, continual; for, as Dufour 
observes, when one of these insects is observed without its being 
disturbed, no scent is perceived; and if, when suddenly seized, it be 
plunged into a fluid, innumerable minute bubbles will be observed to 
issue from two pores between the hind feet, which, on bursting at the 
surface, immediately emit the scent peculiar to the species. The 
species of Reduvii, and other carnivorous species, with strong curved 
beaks, are able to produce, when alarmed, a smart pain, by plunging 
their rostrum into the flesh, and emitting a drop of fluid discharged 
from their salivary glands. Others, at the same time, make a creaking 
noise, by the friction of the fore part of the metathorax within the 
hollowed base of the prothorax. 
A peculiarity occurs in some of these insects, whereof analogous 
instances have already been noticed among the Orthoptera, Homo- 
ptera, Aphide, and even in a species of Chalcididz, namely, the unde- 
veloped state of some specimens in the imago state which are never- 
theless as capable of reproduction as others of the same species which 
have acquired fully developed wings. Thus the bed-bug has never been 
observed but with the minute rudimental upper wings, somewhat re- 
sembling the ordinary wing-cases of pupe ; others, again, as the species 
of Gerris, Hydrometra, and Velia, are mostly found perfectly apterous, 
whilst occasionally they are found with full-sized wings. The winged 
males of Capsus ambulans are stated by Fallen (.Wenogr. Cim. Suec. 
p. 6.) to be always found coupled with apterous females. Chorosoma 
miriformis, Prostemma guttula, Pachymerus brevipennis, &c., are 
generally found with very short wing-covers, but occasionally with 
full-sized wings. 
Two erroneous opinions have been entertained with respect to these 
undeveloped individuals : first, that they are pup, and, consequently, 
that pupe are able to reproduce; and second, that they belong to 
distinct species. Against the first of these opinions, I will only ob- 
serve that the structure of the real pupz of such specimens as subse- 
quently attain wings is quite different from that of these cmperfect 
perfect insects, as they may be called ; and, against the second, I will 
refer to the analogy offered by the other groups above alluded to, and 
to the constant discovery of the winged and imperfect individuals in 
