178 NATURAL HISTORY OF AQUATIC INSECTS CH. 



x^g 



Fig. 6i. — Head of larva of Simulium, 

 ventral view, showing mouth-organs. 

 The eye-spots of the dorsal surface 

 are seen through. 



By the help of a lens the larva can often be seen 

 combine them out with its mandibles. There are two 



pairs of eyes, which are 

 reduced to mere pigment 

 .spots, and small three- 

 jointed antennae. 



There are two pairs of 

 legs, as in the larva of 

 Chironomus, and these end 

 in coronets of hooks. But 

 in the Simulium larva 

 there is no burrow to cling 

 to, and the legs become 

 greatly modified. Each pair 

 coalesces to form a single 

 organ, which is mainly 

 employed as a sucker. The fore pair, borne upon 

 the first thoracic segment, is however occasionally 

 used in grasping, being opposable to the head. The 

 action of these suckers is easily demonstrated by 

 placing a larva fresh from the stream in a saucer of 

 water. It creeps about like a Leech, applying the 

 two ends of its body alternately to the smooth sur- 

 face of the saucer. Even in a rushing stream it 

 appears never to be detached against its will. The 

 hooks, not unlike in form to the hooks found on the 

 legs of the Chironomus larva, form concentric rows 

 on the extremity of the fused legs of the Simulium 

 larva. They are probably useful to prevent slipping 

 upon the smooth leaf or slimy stone. In the suckers 

 of a Cuttle-fish we find the same contrivance resorted 

 to. Each sucker is a cup whose cavity can be en- 



