41 



fuiiftioii is quite obscure: in Machilis it might possibly 

 be analogous with the vagus system of Yertebrata. A 

 somewhat similar system of nerves occurs among various 

 Pterygota, notably in the caterpillars of Cossus lignijjerda 

 (Lyonnet) and Sn/iiihr liyustri (IS'ewpoa't), and in the larva 

 of Chironoinus (Miall and Hammond). 



9. The Sexsory Organs. 



The sensory organs of Anurida consist of the eyes, 

 the post-antennal oi'gan, the apical sense organ of the 

 antennse and sensory hairs. 



The eyes form a group of hve glistening black dots 

 on either side of the head. Each group is situated on a 

 very marked oval protuberance a short distance behind 

 the base of the antenna of its side (Plate I., figs. 1 and 4). 



Each eve, when viewed from above, is seen to be oval 

 in form and somewhat convex, it is invested by the general 

 cuticle of the body-wall, which forms a perfectly smootli 

 and transparent corneal lens. AVhen viewed in vertical 

 section each eye is seen to be shaped very much like an 

 inverted cone (Plate III., tig. 34). Situated immediately 

 beneath the lens are four small cells, which belong to the 

 hypodermis and are directly continuous with it ; they 

 contain no pigment and are full of clear protoplasm. Two 

 of these cells are visible in the figure, and as they secrete 

 the lens they may be termed the lentigen cells. Situated 

 internally to the latter are four very large, deeply pig- 

 mented cells, which together form the retina. The inner 

 ends of these cells pass into and are directly continuous 

 with a branch of the optic nerve. They are invested with 

 a mass of pigmented hypodermis which also fills the 

 interstices between adjacent eyes. 



It will be noted that the eyes of Anurida are 

 structures formed on an extremely simple plan. The 



