74 



THB bbe-kbspbr's GUIDB ; 



are the ocelli. Rarely there are but two ocelli, and very rarely 

 but one. 



The simple eyes (Fig. i,///) are circular, and possess a 

 cornea, lens or cone, and retina, which receives the nerve of 

 sight. 



From the experiments of Reaumur and Swammerdam, 

 which consisted in covering the eyes with varnish, they con- 



FiG. 22. 



Lo7igitudiital Hectioji Slye, — From Cowan. 



c Facet. 

 A Hair. 



re Lenses. 



plp2p-d Rods. 



m Basilar membrane. 

 o Optic nerve. 



eluded that vision with these simple eyes is very indistinct, 

 though by them the insect can distinguish light. Some have 

 thought that these simple eyes were for vision at slight dis- 

 tances. L,ubbock, Forel, and others, are doubtless correct in 

 the view that the ocelli are for near vision, and for use in dark 



