46 The Form of Insects 



situated on the inner face of the drum to the auditory 

 nerve (fig. 29 G) (23, a). 



In many Flies (the Blowfly for example) a some- 

 what similar circular drum, in connection with air- 

 spaces and nerve-endings, is situated in a cavity 

 beneath the base of each wing. Above this drum, 

 under the scutellum, is a supra-tympanal organ, like 

 that of the long-horned Grasshoppers described above. 

 Moreover, chordotonal organs are found in the stalked 

 knobs or "balancers" which represent the hind- wings 

 of Flies. These insects have, therefore, a complex 

 set of hearing-organs, and the fact that the removal 

 of their *' balancers" destroys their power of flight, 

 suggests that the delicate sensations which they thus 

 receive are of the greatest use to them in co-ordinat- 

 ing their movements (4). 



A very beautiful ear is found in the second segment 

 of the feeler in many insects ; this organ is most 

 perfectly developed in the males of certain Gnats and 

 Midges. The segment is greatly swollen and cup- 

 shaped, and somewhat concave on its outer face, where 

 around the base of the next succeeding segment is a 

 ring-shaped plate or drum, which is produced inwardly 

 into numerous processes. These are connected with 

 long rod-like cells united by means of nerve-fibrils 

 with large nerve-cells, which are arranged within the 

 outer wall of the swollen segment and connected 

 with large offshoots from the main nerve of the feeler 

 (fig. 35). In the females of these insects a similar 

 organ is present, but not in nearly so high a state of 

 perfection as in the males. It is evidently of service 

 to the male in enabling him to find a mate. The fine 

 hairs on the shaft of the male's feelers are known to 

 vibrate to the note produced by the humming flight 

 of the female, and to vibrate most strongly when the 

 path of the sound cuts them at right angles — that is, 



