ARTHROPODA 



215 



The median eyes are of the cupulate type with a semi-inverted 

 retina the cells of which are doubled upon themselves ^ (Fig. 127). The 

 lateral eyes have an inverted retina with a tapetum (Fig. 124). 



Fig. 217. — The Pseudoscorpion, Carffosius ischsocbules. 



Showing two simple eyes, S, on either side (specimen from Natural History 

 IMuseum ) . 



HARVESTMEN (PHALAXGIDA ; OPILIONES), minute spider-like 

 Arachnids with extremely long legs, which avoid the glare of daylight, 

 have two simple ocelli mounted one on either side of an oculiferous 

 tubercle (ocularium) (Fig. 218). It would seem that with its laterally 

 directed eyes the animal has no frontal vision. Each ocellus is a simple 



Harvestman 



As^. *** 



Fig. 218. — The Eye of the Harvestman, Megabusus diadem a. 

 The smiple eye is seen on a siDecial oculiferous tubercle (specimen from 

 Natural History Museum). 



cupulate eye with a large cuticular lens and a simple row of visual cells 

 from which the fibres emerge in several branches to form the optic 

 nerve (Purcell, 1894). 



^ p. 1.50. 



