ANURIDA. 393 



function 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 ligniperda 

 (Lyonnetj and Sphinx ligustri (Newport), and in the larva 

 of Chironomus (Miall and Hammond). 



9. The Sensory Organs. 



The sensory organs of Anurida consist of the eyes, 

 the post-antennal organ, the apical sense organ of the 

 antenna? and sensory hairs. 



The eyes form a group of five glisten iug 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 eye, 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 smooth 

 and transparent corneal lens. When viewed in vertical 

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

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

 beneath the lens are four small eells, 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 tills the 

 interstices between adjacent eyes. 



It will be noted that the eyes of Anurida are 

 structures formed on an extremely simple plan. The 



