ANATOMY AND PHYSIOLOGY 



body, (3) retina, (4) nerve fibers, (5) pigmcnted hypodermis cells, and (6) 

 accessory cells, between the retinal cells and the nerve fibers. The lens, 

 usually biconvex in form, is a local thickening of the general cuticula; 

 it is supplemented in its function by the vitreous body, consisting of a 

 layer of transparent hypodermis cells; these in many insects are elongate, 

 constituting a vitreous layer of rather more impor- 

 tance than the one represented 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 retinula. The basal end 

 of each retinal cell is continuous with a nerve fiber 



r 



n 



FIG. 139. Median ocellus of honey bee, Apis mcllifera, in 

 sagittal section. //, hypodermis; /, lens; n, nerve; p, iris pigment; 

 r, retinal cells; v, vitreous body. After REDIKORZEW. 



n 



n 



FIG. 140. An ocel- 

 lar retinula of the honey 

 bee, composed of two 

 retinal cells. A , longi- 

 tudinal section; B, 

 transverse section; u, 

 n, nerves; p, pigment; 

 r, rhabdom. After RED- 

 IKORZEW. 



(Fig. 140), according to Redikorzew and others, 

 and in some instances (Calopteryx) a nerve fiber 

 enters the cell. Each retinula contains a longi- 

 tudinal 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 somewhat 



