42 



AA^ ECONOMIC ENTOMOLOGY. 



arated ; or there may be only two, one on each side, near the 

 base of the antenna, as is usual in butterflies and moths. 



Fig. 22. 



Sensory organs of insects.— yi, one element in eye of a roach ; B, section of compound 

 eye ; C, organs of smell in May-beetles ; D, sense organs in abdominal appendages ; E, 

 sensory ear ; F, ear on foreleg of locust ; G, ear found on the basal segment of grass- 

 hopper abdomen. All greatly enlarged. 



Compound eyes are so termed because they are made up of a 

 great number of simple eyes, or ocelli, set very close together. 

 If the head of a bee or house-fly is examined, it will be noted 

 that the brown eyes occupy a very large portion of its surface, 

 and if one of those eyes be viewed under the microscope it 

 will be found to be faceted, or to consist of thousands of little 

 hexagonal disks, resembling in appearance the top of a honey- 

 comb. Each one of these facets represents a complete eye, 

 capable of forming an image upon its own little retina, and the 

 combination of all the little retinal pictures is what a fly or other 

 insect sees. In some cases the eyes are so enormous that the 

 insect can see everything going on in front, at each side, above 

 and beneath, and even back, except directly behind it. It is 

 difficult for us, who are able to see in one direction only, to 



