SENSES OF INSECTS. 263 
in the common water-beetle [Dytiscus marginalis), but 
with this peculiarity, that it is furnished with a pair of 
nipples. I have before described an analogous part co- 
vered with papilla?, in JEshna viatica, and you will find 
it in other insects 3 . Perhaps at first this part may seem 
merely a continuation of the palate ; but if you consider 
the peculiarities in its structure just noticed, it is evi- 
dently a sensiferous organ ; and as the sense of smell ap- 
pears to reside in the head, this is its most probable seat. 
But by what channel scents act upon it, — whether they 
are transmitted through the pores of the part represent- 
ing the nostrils, or received by the mouth, — I will not 
venture to assert positively : but from the circumstance 
of their being membranous in some insects remarkable 
for acute scent, as in NccropJwrus, Staphi/linus, &c, there 
seems some ground for the former opinion, which re- 
ceives further confirmation from an observation of an 
eminent Comparative Anatomist, M. Cams, with respect 
to Acrida verrucivora, in which under the nose and 
rhinarium, as appears from his description, he found 
some tracheae, and two lobes of the cerebral ganglion, 
which caused him to regard this as the seat of the sense 
of smell b . He also tells us that Rosenthal, in the blue- 
bottle-fly (Musca vomitoria) places the sense of smell 
partly in a delicately folded membrane observable in its 
head c . As the sense of smell in these little beings is ex- 
tremely acute, as well as their hearing, the perception of 
odours may reach their sensory through the above pores; 
* Vol. III. p. 454—. 
b Introd. to Comp. Anat. i. 76. The part he alludes to, is figured 
Plate VI. Fig. 4. a. g\ 
Iltid, This membrane likewise represents the Nose and Rhina- 
rium in that fly. 
