9 6 



ENTOMOLOGY 



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 elon- 

 gate, constituting a vitreous layer of rather more importance than the 

 one represented in Fig. 141. 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 (Fig. 

 142), according to Redikorzew and others, and in 



* 



B "-r 



FIG. 141. Median ocellus of honey bee, -Apis mellifera, in 

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

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



FIG. 142. An ocel- 

 lar retinula of the honey 

 bee, composed of two 

 retinal cells. A, longi- 

 tudinal section; B, 

 transverse section; n, 

 n, nerves; p, pigment; 

 r, rhabdom. After RED- 

 IKORZEW. 



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. Pig- 

 ment 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 

 the same plan as the human eye, its capacity for forming images must 



