448 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



of which is embedded in a central pigment body, and 

 surrounded by fine cylindrical optic cells, which form 



Figs. 191 A, 191 c. Figures of Eyes of Arthropoda. 



A, Eye of larva of Dytiscus, showing the simplest condition of a single layer of 

 cells (p, a, r), continuous with those of the hypodermis (to) ; each cell is dis- 

 tinct, and some (r) are continuous with optic nerve fibres (o) ; I, lens. (After 

 Grenacher.) 



c, Simple eye (sternum) of fly, showing the layer (gk) of vitreous cells distinct 

 from the retinal layer (rt) ; c, cuticle; hyp, hypodermis ; I, lens ; fg, fat cells; 

 tt\ trachea ; on, optic nerve ; og, optic ganglion ; st, rods of retina. (After 

 Grenacher.) 



a retina ; each of these cells is sharply divided into 

 two portions ; that which lies nearest the lens is rod- 

 like, the rest is granular in character. As the lenses 



