122 NATURAL HISTORY OF AQUATIC INSECTS CH. 



slight dilatations of the air-tubes. In Mochlonyx 

 they are greatly enlarged, and the connecting air- 

 tubes reduced in diameter, though filled with air. In 

 Corethra the vesicles are the only reservoirs of air, 

 the connecting tubes, though visible by the micro- 

 scope, being filled with a watery fluid. The Moch- 

 lonyx larva retains in a reduced form the breathing- 

 tube, which is so conspicuous in Culex, and which 



FIG. 36. Head of Fly of Corethra. The antennae (except their enlarged basal joints) 



are cut away. 



disappears in Corethra. These and other facts of the 

 same kind seem to indicate that the three larvae have 

 diverged from a common form, but what that common 

 form was I do not venture to conjecture. 



CHIRONOMUS. 



One of the commonest, and certainly one of the 

 most instructive, of aquatic Insects is the larva of 

 Chironomus. It abounds in ditches, water-butts, and 

 streams, especially dirty streams, and feeds upon 

 decaying vegetable matter. It may be readily recog- 

 nised by its crimson colour, which has suggested the 



