EYES AND SIGHT, 
99 
bi-convex lens, or corneule^ chitinous and perfectly 
transparent. Beneath each is placed the crystalline 
cone (c c) ensheathed by pigment cells. The crystal- 
line cone has been carefully studied by Claparede 
Fig. 44. — Longitudinal Section through Compound Eye. 
(25), and found by him to consist of from four to 
sixteen original, but completely combined segments, 
secreted by cells which lie immediately behind each 
facet, but of which, when the eye is completely de- 
veloped, only the nuclei (Fig. 45, n) (known as 
Semper’s nuclei) finally remain. 
Grenadier (57) divides the compound eyes of 
