MOTIONS OF INSECTS. 281 



and dilatation ; but are able, by various serpentine con- 

 tortions, aided by their mandibles, to move in the sub- 

 stance which constitutes their food. Should any acci- 

 dent remove 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 fixing it 

 firmly, and then suddenly resuming a rectilinear posi- 

 tion, 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 proba- 

 bly act ns a sucker, and so be more firmly fixable a . 

 The grub of a fly whose proceedings in that state I have 

 before noticed 5 (Leptis Vermileo\ will, when removed 

 from its habitation, endeavour to recover it by leaping. 

 Indeed this mode of motion seems often to be given to 

 this description of larvae by Providence, to enable them 

 to return to their natural station, when by any accident 

 they have wandered away from it. 



Many apodous larvae 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 tor- 

 ments, compels us to feel some curiosity about its history. 

 Its larva is a very singular creature, furnished with a 

 remarkable anal apparatus for respiration, by which it 

 usually remains suspended at the surface of the water. 

 a De Geer, vi. 389 b VOL. I. 431. 



