78 Till: UN-] STORY OF INSECTS [CH. 



to fix tlio larva in the muddy tube which it inhabits 

 at the bottom of its native pond. The penultimate 

 abdominal segment has four long hollow outgrowths, 

 which contain blood, and have the function of gills, 

 while the hindmost segment has four shorter out- 

 growths of the same nature. f]nabled thus to breathe 

 dissolved air, the Chironomus larva needs not, like 

 the Culex or the Eristalis, to find contact with the 

 atmosphere beyond the surface-film. 



Most remarkable, in many respects, of all aquatic 

 larvae are the grubs of the Sand-midges (Simulium). 

 These live entirely submerged and, having no special 

 gills, carry out an exchange of gases through the 

 general surface of the cuticle between the dissolved air 

 in the water and the cavities of the air- tube system. 

 The body is shaped like a flask swollen slightly 

 at the hinder end and possesses a median pro-leg 

 just behind the head, also another at the tail, which 

 serves to attach the larva to a stone or to the leaf 

 of an aquatic plant. The head has, in addition to 

 feelers and jaws, a pair of processes with wonderful 

 fringes which by their motion set up currents in the 

 water, and bring food particles within reach of the 

 mouth. A number of the larvae usually live in a 

 community. Their power of spinning silken threads 

 by which they can work their way back when acci- 

 dentally dislodged from their resting-place, has been 

 vividly described by Mjall (1895). 



