INSECTA 123 



Hearing. — Many insects have sound-producing organs and 

 auditory organs ; and it has been proved by experiment that they 

 hear. The ear of the grasshopper or locust, a small tympanic 

 membrane, is situated at the anterior end of the abdomen, while 

 that of the katy-did and cricket (Fig. 95) is situated on the tibia 

 of the fore-leg. There is a special auditory ganglion. The 

 mosquito has its auditory organs in the antennae in the seg- 

 ments next to the basal ones, through which the sound or vibra- 

 tions are carried by many fine auditory hairs, and from which the 

 auditory nerves lead to the "brain." It is thought that the 

 male mosquito finds his mate by her song. 



Sight. — Insects usually have both simple and compound 

 eyes, though either kind may be found alone; and a few in- 

 sects are blind by degeneration. The ocelli, or simple eyes, 

 are usually three in number and form a little triangle on the 



Fig. 95. — The front leg of the cricket enlarged, showing the ear at a. 



top of the head. Each of them is supplied with a special nerve 

 from the " brain." It is thought that the ocelli can do little 

 more than distinguish light from darkness and that their range 

 of vision is restricted to an inch or two in front of the head. 

 The compound eyes, two in number (see Fig. 84), are usually 

 large and conspicuous, often composing more than two-thirds 

 of the entire head. Each compound eye presents from twenty 

 to several thousand polygonal facets, or windows, which, alto- 

 gether, form the cornea. It is thought that the range of vision 

 of the compound eyes is two or three yards. The larger the 

 eyes, the wider will be the range of vision, while the smaller 

 and more numerous the facets, the sharper and more distinct 

 will be the image. Experim^ent and study of the structure of the 

 eye, says Kellogg, " indicate that, at best, the sight of insects 

 cannot be exact or of much range." 



