SURROUNDINGS OF GROWING INSECTS 193 



(Fig. 101 a b) that live in swift clear streams, and these little 

 blackish grubs are said to die in a few hours if transferred from 

 their native torrents into still water. They build no tube or other 

 shelter, but spend much of their time attached to water-plants 

 or submerged stones by means of a sucker-process at the hinder 

 end of the body, which is probably formed by the union of a 

 pair of tail prolegs. Similarly the prolegs on the prothorax, 

 which in the Chironomus larva retain their normal paired 

 condition, are in the Simulium larva, joined together to form 



FIG. IOI. 



a, Larva of Sandfly (Simulium), side view ; b, dorsal view ; c, Pupa (ventral view) ; d, dorsal view. 

 X 7. e, cocoon, x 4. From Osborn, U.S. Dept. Agric. Ent. Bull. 5, after Verdat. 



a short median limb, so that this grub can move about after 

 the manner of a leech or a " looping " caterpillar. Besides 

 its short feelers and the usual series of jaws mandibles, 

 maxillae and labium the head of the sandfly larva is provided 

 with a pair of beautifully fringed plates, known as the " fans ' 

 or " brushes ". These serve to waft into its mouth the micro- 

 scopic plants and Crustacea which furnish its food-supply. 

 In the rush of the well-aerated water that it inhabits, the larva 

 needs no special breathing organs. The salivary secretion, 

 discharged from the mouth, forms a silken thread, and the 



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