MOTIONS OF INSECTS. 473 



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), will, 

 when removed from its habitation, endeavor 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 larvee inhabit the water, and therefore must be furnished 

 with means of locomotion proper to that element. To this class belongs 

 the common gnat (^Culcx plpiens), which, being one of our greatest tor- 

 ments, compels us to feel some curiosity about iis 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. 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 con- 

 tortions of the upper and lower halves of it, and thus it moves with much 

 celerity. The laminae or swimmers, which terminate its anus-, 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 dipterous 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 surface 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.^ — A well-known fly (^Strati/omis 

 Chamceleon), in its first state an aquatic animal, ofien 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 bub- 

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

 horizontally, it bends its body alternately to the right and left, contracting 

 itself into the form of the letter S ; and then extending itself again into 

 a straight line, by these alternate movements it makes its way slowly in 

 the water.^ 



I have dwelt longer upon the apodous larvae, or those that are without 

 what may be called proper legs, analogous to those of perfect insects, 

 because the abscence of these ordinary instruments of motion is in num- 

 bers of them supplied in a way so remarkable and so worthy to be known ; 

 and because in them the wisdom of the Creator is so conspicuously, or, I 

 should rather say, so strikingly manifested, since it is, doubtless, equally 

 conspicuous in the ordinary routine of nature. But aberrations from her 

 general laws, and modes, and instruments of action, often of rare occurrence, 

 impress us more forcibly than any thing that fiiUs under our daily obser- 

 vation. 



» De Geer, vi. .^89. 2 Reaum. iv. t. 43. f. 3. nn. 



» De Geer, vi. 375. t. xxiii. f. 4, 5. * Swamra. Bibl. Nat. Ed. Hill, ii. 44. b. 47. a. 



40* 



