INSECTA. 211 



All Mandibulate insects have a process from the labium, within 

 the mouth, so analogous to a tongue as to have received that name. 

 It is particularly well developed in the dragon-fly and grasshopper, in 

 which its soft, finely ridged, upper surface receives a rich supply df 

 nerves. It is not present in the suctorial insects, which, as Burmeister 

 well observes, always subsist upon one and the same food, generally 

 inhabit what they feed on, and consequently less require the sense of 

 taste. 



Although a few physiologists have suspected that some part or 

 appendage of the head, and others that the membranous lining of 

 the spiracles were the organs of smell, the precise seat of that sense, 

 which unquestionably exists in insects, has not yet been experi- 

 mentally determined. The application by the common house-fly of the 

 sheath of its proboscis to particles of solid or liquid food before it 

 imbibes them, is an action closely analogous to the scenting of food 

 by the nose in higher animals : and as it is by the odorous qualities 

 much more than by the form of the surface, that we judge of the 

 fitness of substances for food, it is more reasonable to conclude that 

 in this well-known action of our commonest insect, it is scenting, 

 not feeling, the drop of milk or grain of sugar. But no one ever 

 saw an insect present its spiracles to a nutritive substance before 

 feeding. 



The signs of attention and hearing are plainer in insects than 

 those of smelling ; yet the precise organ has not yet been more defi- 

 nitely recognised, unless the structure, peculiar, however, to moths, 

 described by Treviranus, be the true seat of the auditory sense ; it 

 consists of a simple drum situated in front of the base of each an- 

 tenna. It is strange, however, that the organ under so well marked a 

 form should not exist in crickets, tree-hoppers ( Cicadcs), and other 

 insects which attract their females by jjeculiar notes. Onlj^ the soft 

 capsular membrane of the joint of the antenna, which in some move- 

 ments may be rendered tense, has been alluded to by Burmeister as 

 a structural indication of the organ of hearing in the peculiar ap- 

 pendages in which he supposes, with most other entomologists, that 

 the sense resides. The acoustic nerve quits the antennal nerve, in the 

 Crustacea, as if it were a branch of that nerve. Two, at least, and 

 often more numerous nervous filaments from a slight ganglionic en- 

 largement, penetrate the antennas in insects ; and these may sub- 

 serve the distinct offices of the appreciation of the vibrations of sound, 

 of the characters of surface, and of the regulation of the movements 

 of the antennae. 



Of all the organs of the special senses not only is that of sight 



p 2 



