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 papillae, in JEshna viatica, and you will find 

 it in other insects a . 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 Necrophorus, Staphylinus, &c., there 

 seems some ground for the former opinion, which re- 

 ceives further confirmation from an observation of an 

 eminent Comparative Anatomist, M. Carus, 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; 



a VOL. III. p. 454. 



b Introd. to Cornp. Anat. i. 76. The part he alludes to, is figured 

 PLATE VI. FIG. 4. a. g'. 



c Ibid. This membrane likewise represents the Nose and Rhina- 

 rium in that fly. 



