THE EYES OF INSECTS 



117 



The simple eyes, or ocelli, have been described by Grenadier, Lowne, 

 Gunther, and others, and their structure has already been alluded to in the 

 description of the ocellus of a young larva of the beetle, Dytiscus (Fig. 4, 



^-ant 



A B 



Fig. 78. — The Heads of Larva of Dytiscus Marginalis, showing Two 



Stages of Development. 



A — Aquatic larva. 



B — Larva about to pupate. 



mx. 2 : second maxilla. 

 oc. c. : rudiment of compound eye. 

 oc. s. : simple ocelli. 

 oc. s. 1 : lenses of the simple eyes, 

 carried away by the loosening of 

 the cuticle. 



ant. 

 es. : 

 es. 1 



antenna. 

 : eye-spot of larva. 

 1 : lens of eye-spot carried away 

 by loosening of the cuticle. 



mn. : mandible. 



mx. 1 : first maxilla. 



(After Gunther, from MacBride.) 



Chap. I, p. 10) ; in this a biconvex " corneal-lens " is formed by a 

 thickening of the cuticle which lies over the elongated distal ends of 

 specially modified hypoderm cells. These converge to the central axis 



Fig. 79. — Vertical Section through Rudiment of Compound Eye — 

 " Imaginal Disc " — of Dytiscus Marginalis, showing First Differentia- 

 tion of Retinula. (After Gunther.) 



ect. : unaltered ectoderm. 



pr. z. : proliferating zone of cell elements at margin of disc. 



ret. : retinulaj. 



or potential cavity of the eye and they form a refractile vitreous body. 

 Deep to the vitreous is the retina composed of elongated sensory cells, 

 which are continuous laterally with the cells of the vitreous and thus with 



