e J°, id - cirf. 



B 



crx. 



P9-- 



omm. 



?°P<g- 



vt. 



D 



Fig. 166.— The eye of the crayfish. 



A, The left eye removed ; B, a portion of the cornea magnified to show the facets ; 

 C, a longitudinal section of the eye under low magnification ; D, a single 

 ommatidmm highly magnified. — D after Parker. 



cr.c, Outer refractive body or crystalline cone ; cu.f. t cuticular facet ; eptd., epidermis 

 (hypodermis) ; mus., muscles which move the eye; n.f., nerve fibres; omm., 

 ommatidia ; oj>.g., optic ganglion ; op.n., optic nerve ;/.£■., outer pigment cells ; 

 p^f., inner pigment cells ; ret., retinula cells (the sense cells)— these cells 

 contain pigment ; r/i., inner refractive body or rhabdome ; vt., vitrellae or cells 

 which secrete the crystalline cone. 



262 



