THE SENSES OF INSECTS 105 



the inner wall of which forms a tympanum or " drum,'' 

 which is in connection with air-spaces and nerve-endings. 

 In some species, however, the tympanum is not in a 

 covered chamber, but at the bottom of an oval depression. 

 Among short-horned grasshoppers an auditory apparatus, 

 comprising one large drum, is found on each side of the 

 first abdominal segment ; while in many two-winged flies 

 a circular drum, connected with nerve-endings, is situated 

 in a cavity beneath the base of each wing. The structure 

 of all these strangely placed organs is very complex ; but 

 those who have examined them admit that they are 

 admirably adapted to receive and transmit sound- 

 waves ; and there can be no doubt that they serve the 

 sense of hearing. There are also organs situated in the 

 antennae of many insects, notably the males of certain 

 gnats and midges, the function of which is thought to be 

 auditory. 



In addition to specialised eyes and ears, insects possess 

 an enormous number of " end-organs " — minute pits, pegs, 

 hairs, and cones of very varied form — which are connected 

 with sensory nerves. These may be found on all parts of 

 the body, but they are most numerous in the neighbour- 

 hood of the mouth, and on the joints of the antennae. We 

 must not forget that the chitinous covering of the insect, 

 which we have likened to a suit of armour, is a hard, dead 

 substance. It has no nerves distributed in it, but is 

 pierced with minute pores through which the end-organs 

 communicate with the nerves. The precise functions of 

 the various structures are naturally very difficult to deter- 

 mine, but it is thought that while many of those on the 

 mouth-parts serve a sense of taste, others on the antennae 

 and palpi are organs of touch and smell. There is also 

 reason for thinking that many insects without specialised 

 ears detect sound-waves by means of end-organs situated 



