Eyes — Ears 43 



being developed to a degree almost inconceivable by 

 us. There is reason to believe that the compound 

 eyes do not perceive objects at a greater distance than 

 six feet ; while there is no doubt that they are able 

 to appreciate colour sensations, since experiments have 

 proved that insects distinguish between colours, and 

 that they show preference for some colours over others 

 (I, 21, 22). 



Ears. — The ears of insects are far less conspicuous 

 than their eyes •, indeed it is only in a few cases that 

 evident organs of hearing are to be found, and none 

 seem to have been observed in the Cockroach. In 

 many insects, however, fine rods have been noticed 

 hung between two points of the skin in various seg- 

 ments of the body and limbs (23, b). These rods are 

 connected with nerve fibres and are believed to receive 

 and transmit sound-vibrations ; they are known as 

 chordotonal organs (fig. 33 D). In the long-horned 

 Grasshoppers and Crickets a number of such rods 

 are found associated together, forming with other 

 structures a complex ear (figs. 29 F, 34), which is 

 situated in the front shin just below the knee-joint. 

 The shin, in these insects, is seen to be swollen at 

 this region, and two slightly curved slits (fig. 34 aa) 

 run lengthwise along the swollen part. These slits 

 open into chambers formed by the inpushing of the 

 skin of the leg ; the chambers are thick-walled out- 

 wardly, but their inner walls are thin, forming two 

 oval drums, each of which is in contact with the wall 

 of an air-tube, the main air-tube of the leg dividing 

 into two branches which join again lower down. 

 Along the outer wall of one of these branches runs a 

 ridge (fig. 34 ca) in which are arranged, in linear 

 series, the cone-shaped endings of the nerve-fibres, 

 each capped by a large cover-cell ; these nerve-endings 

 and their cover-cells decrease in size from top to 



