448 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



of which is embedded in a central pigment body, and 

 surrounded by fine cylindrical optic cells, which form 



ffk 



X 



A 



Pigs. 191 A, 191 C. Figures of Eyes of Artliropoda. 



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

 cells (p, </, r), continuous with those of the hypodermis (ft) ; each cell is dis- 

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

 Grenacher.) 



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

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

 tr t trachea; OM, 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 



