STRUCTURE OF INSECTS. 263 



Auditory (or chordotonal) organs have been found in all 

 orders of Insects (except as yet the Thysanoptera), and 

 occur both in the larvae and in the adults. Their essential 

 structure is as follows : a nerve ends in a centre or ganglion 

 near the skin, some of the cells of this ganglion grow out into 

 long sensitive rods enclosed in a tiny sheath, the rods are 

 directly or indirectly connected with epidermis above them. 

 " They are found in groups of 2-200 in various parts of the 

 body, antennse, palps, legs, wings, in the halteres of Diptera, 

 and upon the dorsal aspect of the abdomen." Quite different 

 from these, and occurring in flies alone, on the hind end of 

 the larva, or at the base of the adult's feelers, are little bags 

 with fluid in which clear globules float. We do not know how 

 much or how little Insects hear, but the "song" of male 

 Cicadas and crickets does not fall on deaf ears. 



In addition to the "eyes" and "ears" there are innervated 

 hairs (tactile, tasting, olfactory) on the antennae and mouth- 

 parts of many insects. Not a few have been shown to possess 

 a diffuse or dermatoptic sense, by which, for instance, they 

 can, when blinded, find their way out of a dark box. 



Many Insects produce sounds which often express a 

 variety of emotions. We hear the whirr of rapidly moving 

 wings in flies, the buzz of leaf-like structures near the 

 openings of the air-tubes in many Hymenoptera, the scraping 

 of legs against wing-ribs in grasshoppers, the chirping of male 

 crickets which rub one wing against its neighbour, the piping 

 of male Cicadas which have a complex musical instrument, 

 the voice of the death's-head-moth which expels air forcibly 

 from its mouth. The death-watch taps with his head on 

 foreign objects, as if knocking at the door behind which his 

 mate may be hidden. In some cases the sounds are simply 

 automatic reflexes of activity ; in many cases they serve as 

 alluring love-songs, and they may also serve as expressions of 

 fear and anger, or as warning alarms. 



Alimentary System. — The diet of Insects is very varied. 

 Some, such as locusts, are vegetarian, and destroy our crops ; 

 others are carnivorous (we need not specify the homoeo- 

 pathist's leech) and suck the blood of living victims, or 

 devour the dead ; the bees flit in search of nectar from flower 

 to flower, while the ant-lion lurks in his pit of sand for any 

 unwary stumbler ; the termites gnaw decaying wood, and 



