300 ANATOMY. 



198. 



Everybody will admit that insects, more than many other animals, 

 require a peculiar organ of touch, from their being encased in a hard 

 insensible integument. It is true the antennae have long had this func- 

 tion ascribed to them, but incorrectly ; the hard horny antennae may 

 possibly well detect the presence of objects, but certainly arrive at no 

 other precise perception, for this requires a soft organ clothed with a 

 very delicate covering. Straus Durkheim * therefore justly wonders 

 how this function could have been ascribed to the antennae ; but he 

 astonishes us still more by considering the still harder feet as organs of 

 touch. By far the majority of insects have hard, horny, perfectly 

 closed foot-joints, and the few which are furnished with setae, feathers, 

 or pulvilli at their plantae or apex of their tarsi do not use them as 

 organs of touch, but merely to assist in climbing ; indeed, there are 

 some genera Avhose feet have soft fleshy balls (Xenos, T/trips, Gryllus, 

 Locusta), but these instances cannot prove it throughout an entire 

 class. For the rest, his opinion loses still more probability, when, 

 instead of his tarsal joints other organs can be shown as instruments 

 of touch. These organs are the palpi, already indicated by their name. 

 If we inspect the palpi of the larger insects, for example, of the pre- 

 datory beetles, the grasshoppers, humble-bees, and many others, we 

 observe at its apex a white, transparent, distended bladder, which, after 

 the death of the creature, dries into a concavity seated at the apex of 

 the palpus. This bladder is the true organ of touch, the main nerve of 

 the maxillae and of the tongue spreads to it, and distributes itself upon 

 its superior surface with the finest branches. Straus f, who carefully 

 observed this bladder, explains it as a sense of a peculiar description, 

 analogous to the taste-smell sense (Geruchsgeschmackssinn) of the 

 Ruminantia, discovered by Jacobson, but just as little as a union of the 

 senses of smell and taste conditionates the presence of a peculiar sense 

 may we explain the palpi as sensual organs of a peculiar description : they 

 are, whence they were named, namely, purely organs of touch. The defi- 

 ciency of palpi in haustellate insects may be objected to here ; but have 

 not these in their long proboscis a better organ of touch, and do not we 

 find everywhere in nature in all the organs an evident adaptation to 



* Considerations, p. 425. f Ibid., p. -i'27. 



