THE ORGANS OF THE SENSES. 297 



196. 



Much more doubt and uncertainty attends the observations and 

 opinions upon the organ of smell of insects. Reaumur, Lyonet, and 

 several modern French naturalists, consider the antennae as such., but 

 I would ask with what right ? A hard, horny organ., displaying no nerve 

 upon its surface, cannot possibly be the instrument of smell, for we 

 always find in the olfactory organ a soft, moist, mucous membrane, fur- 

 nished with numerous nerves. No such tunic is to be found in insects, 

 at least in their head, or upon the surface of their bodies. Marcel de 

 Serres*, and before him, Bonnsdorf f, endeavoured to prove the palpi 

 organs of smell, he described pores at their extremities, namely, in the 

 Orthpptera, which passed through its soft apex into the interior, and 

 here distributed nervous branches ; he also considered that the tracheae 

 of the palpi opened into the mouth, and that thereby a constant stream 

 of air was kept through them; but it is all fanciful without any 

 satisfactory foundation. The palpi have no pores at their extremity, 

 and their tracheae have no external orifice Comparetti J found 

 cavities and cells beneath the frons, which nobody ever saw, either 

 since or before, and these he considers organs of smell. More recently, 

 F. Rosenthal described a folded skin at the forehead, beneath the 

 antennae, to which two fine nerves passed, and which he considers as 

 the organs of smell of Musca domestica and vomit oria; and he observed, 

 after the destruction of the part, a deficiency of the function which had 

 previously strongly exhibited itself. But it is with this as with the 

 discovery of the organ of hearing in Blatta ; we cannot reason from it, 

 as similar structures have not been observed in other insects, and pre- 

 cisely in the dung beetles, which have the sense so acute, the forehead 

 is covered with a horny shield, that it is wholly impossible odours should 

 pass through it. Indeed, in the burying beetles (Necrophori), which 

 decidedly possess the most acute smell of all the Coleoptera, have above 

 the mouth, upon the clypeus, a triangular yellow somewhat deep spot, 

 having the appearance of a membrane stretched over it, and this 

 might be considered the analogue of the organ of smell discovered by 

 Rosenthal ; but, upon closer inspection, this spot appears to consist 

 also of a horny material, and we therefore cannot conceive it possible 



* Annal. du Mus. T. : xviii. pp. 426 441. 



t De fabrica et usu Palporum in Inscctis. Aboa;, 1792. J Sdielvcr, p. 46.. 



Reil's Arcliiv. Vol. x. p. 427. 



