THE SPECIAL SKXSES 



41 



compound eyes, situated on the sides of the head, are 

 composed of numerous simple eyes, which are complex 

 in structure. The number of simple eves in the com- 

 pound eye varies in different, insects. The ant has 

 about fifty simple eyes in its compound eye. The 

 compound eye of the dragon-fly (Fig. 26) contains 



FIG. 25. Fragment of outer surface 

 (cornea) of eye of dragon-fly, much 

 enlarged, showing the hexagonal fac- 

 ets. Drawn from nature by Miss M. 

 E. Wise. 



FIG. 26. Head of dragon-fly. En- 

 larged, to show well-developed com- 

 pound eyes forming sides and upper 

 part of head. From a photograph. 



20,000 simple eyes. In the compound eye, the outer 

 surface or cornea of each simple eye is hexagonal. 

 These hexagonal surfaces are joined together, form- 

 ing a many-faceted cornea for the compound eye (Fig. 

 27). These eyes composing the compound eye see in- 

 dependently of eaeli other. Each one is aide to see but 

 a small part of any object before the compound eye, so 

 that insects see images and objects not as entire things, 

 but in mosaic; that is, the object viewed seems to 

 the insect to be composed of many small independent 

 parts. 



Some insects do not have eyes. Those insects which 

 live constantly in the dark, such as those which are 



