ANATOMY AND PHYSIOLOGY 



109 



FIG. 139. 



i 



While the lateral ocelli are comparatively simple in structure, 

 consisting of a small number of cells, the dorsal ocelli almost 

 rival the compound eyes in complexity. 



Dorsal Ocelli. These consist (Fig. 139) of (i) lens, (2) 

 vitreous body, (3) retina, 

 (4) nerve fibers, (5) pig- 

 mented hypodermis cells, 

 and (6) accessory cells, be- 

 tween the retinal cells and 

 the nerve fibers. The lens, 

 usually biconvex in form, is 

 a local thickening of the 

 general cuticula; it is sup- 

 plemented in its function by 

 the vitreous body, consist- 

 ing of a layer of transpar- 

 ent hypodermis cells; these 

 in many insects are elon- 

 gate, constituting a vitreous 

 layer of rather more im- 

 portance than the one rep- 

 resented in Fig. 139. The 

 retina consists of cells more 

 or less spindle-shaped and 

 associated in pairs or in groups of two or three, each group 

 being termed a rctinula. The basal end of each retinal cell is 

 continuous with a nerve fiber (Fig. 140), according to Redi- 

 korzew and others, and in some instances (Calopteryx) a nerve 

 fiber enters the cell. Each retinula contains a longitudinal rod, 

 or rhabdom, in the secretion of which all the cells of the retinula 

 are concerned. Between the retinal cells and nerve fibers are 

 indifferent, or accessory cells. Pigment granules, usually black, 

 are contained in these cells, also in the retinal cells and around 

 the lens, in the last instance forming the iris. 



Vision by Ocelli. Though the ocellus is constructed on 



Median ocellus of honey bee, Apis mel- 

 lifera, in sagittal section, h, hypodermis; 

 I, lens; n, nerve; p, iris pigment; r, retinal 

 cells; v, vitreous body. After REDIKORZEW. 



