284 MOTIONS OF IXSCCTS, 



larvae, which inhabit horse-dung, though deprived of 

 feet, cannot move by annular contraction and dilata- 

 tion ; but are able, by various serpentine contortions, 

 aided by their mandibles, to move in the substance 

 which constitutes their food. Should any accident re- 

 move them from it. Providence has enabled them to 

 recover their natural station by the power I am speak- 

 ing of. When about to leap, they do not, like the 

 cheese-fly, erect themselves so as to form an angle with 

 the plane of position ; but lying horizontally, they 

 bring the anus near the head, regulating the distance 

 by the length of the leap they mean to take ; when fix- 

 ing it firmly, and then suddenly resuming a rectilinear 

 position, they are carried through the air sometimes 

 to the distance of two or three inches. They appear to 

 have the power of flattening their anal extremity, and 

 even of rendering it concave ; by means of which it 

 may probably act as a sucker, and so be more firmly 

 fixable*. — The grub of a fly, whose proceedings in that 

 state I have before noticed'' (Leptis Vermileo^ F.), will, 

 when removed from its habitation, endeavour to re- 

 cover it by leaping. Indeed this mode of motion seems 

 often to be given to this description of larvaB by Pro- 

 vidence, to enable them to return to their natural sta- 

 tion, when by any accident they have wandered away 

 from it. 



Many apodous larvae inhabit the water, and there-'t 

 fore must be furnished with means of locomotion proper 

 to that element. To this class belongs the cojnmon 

 gnat (Culex pipiens, L,), which being one of our great- 

 est torments, compels us to feel some curiosity about 



• De peer, vi. 389— " Vol, I. 2(1 Ed. 432. 



