230 MOTIONS OF INSECTS. 



Indeed this mode of motion seems often to be given to this 

 description of larvas by Providence, to enable them to return 

 to their natural station, when by any accident they have 

 wandered away from it. 



Many apodous larvse inhabit the water, and therefore must 

 be furnished with means of locomotion proper to that element. 

 To this class belongs the common gnat ( Culex pipiens), which, 

 being one of our greatest torments, compels us to feel some 

 curiosity about its history. Its larva is a very singular crea- 

 ture, furnished with a remarkable anal apparatus for respir- 

 ation, by which it usually remains suspended at the surface 

 of the water. If disposed to descend, it seems to sink by the 

 weight of its body ; but when it would move upwards again, 

 it effects its purpose by alternate contortions of the upper 

 and lower halves of it, and thus it moves with much celerity. 

 The laminas or swimmers, which terminate its anus 1 , are 

 doubtless of use to it in promoting this purpose. It does not, 

 that I ever observed, move in a lateral direction, but only 

 from the surface downwards, and vice versa. — Another dip- 

 terous larva (Corethra culiciformis), which much resembles 

 that of the gnat in form, differs from it in its motions and 

 station of repose ; for, instead of being suspended at the sur- 

 face with its head downwards, it usually, like fishes, remains 

 in a horizontal position in the middle of the water. When it 

 ascends to the surface, it is always by means of a few strokes 

 of its tail, so that its motion is not equable, sed per saltus. 

 It descends again gradually by its own weight, and regains 

 its equilibrium by a single stroke of the tail. 2 — A well-known 

 fly (Stratyomis Chamceleon), in its first state an aquatic ani- 

 mal, often remains suspended, by its radiated anus, at the 

 surface of the water, with its head downwards. But when 

 it is disposed to seek the bottom or to descend, by bending 

 the radii of its tail so as to form a concavity, it includes in 

 them a bubble of air, in brilliancy resembling silver or pearl ; 

 and then sinks with it by its own weight. When it would 

 return to the surface it is by means of this bubble, which is, 

 as it were, its air-balloon. If it moves upon the surface or 



1 Iteaum. iv. t. 43. f. 3. nn. 



2 De Gcer, vi.375. t. xxiii. f. 4,5. 



