MOTIONS OF INSECTS 437 



vortex thus produced. As these animals require to be firmly fixed to the 

 substance on which they take their station, and their back is the only part, 

 when they are doubled as just described, that can apply to it, they are fur- 

 nished with minute legs armed with black claws, by which they are enabled 

 to adhere to it. They have ten of these legs : the four anterior ones, which 

 point towards the head and are distant from each other, are placed upon 

 the fourth and fifth dorsal segments of the body ; and the six posterior ones, 

 which point to the anus and are so near to each other as at first to look 

 like one leg, are placed on the eighth, ninth, and tenth. When the animal 

 moves, the body continues bent, and the sixth segment, which is without 

 feet, and forms the summit of the curve, goes first. 1 De Geer named the 

 fly it produces Tipula amphibia : it seems not clear, from his figure, to which 

 of the modern genera of the Tipulanas it belongs ; nor is it referred to by 

 Meigen. 



I come now to the jumping apodes ; and one of this description will 

 immediately occur to your recollection, that I mean which revels in 

 our richest cheeses, and produces a little black shining fly (Tyrophaga 

 Casei). These maggots have long been celebrated for their saltatorious 

 powers. They effect their tremendous leaps laugh not at the term, for 

 they are truly so when compared with what human force and agility can 

 accomplish in nearly the same manner as salmon are stated to do when 

 they wish to pass over a cataract, by taking their tail in their mouth, and 

 letting it go suddenly. When it prepares to leap, our larva first erects 

 itself upon its anus, and then bending itself into a circle by bringing its head 

 to its tail, it pushes forth its unguiform mandibles, and fixes them in two 

 cavities in its anal tubercles. All being thus prepared, it next contracts its 

 body into an oblong, so that the two halves are parallel to each other. 

 This done, it lets go its hold with so violent a jerk that the sound produced 

 by its mandibles may be readily heard, and the leap takes place. Swam- 

 rnerdam saw one, whose length did not exceed the fourth part of an inch, 

 jump in this manner out of a box six inches deep ; which is as if a man six 

 feet high should raise himself in the air by jumping 144 feet ! He had 

 seen others leap a great deal higher. 2 The grub of a little gnat lately 

 noticed (Chironomus stercorarius') has a similar faculty, though executed in 

 a manner rather different. These larvas, which inhabit horse-dung, though 

 deprived of feet, cannot move by annular contraction and dilatation ; but 

 are able, by various serpentine contortions, aided by their mandibles, to 

 move in the substance which constitutes their food. Should any accident 

 remove them from it, Providence has enabled them to recover their natural 

 station by the power I am speaking 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 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. 3 The grub of a fly, whose proceedings in 



1 De Geer, vi. 380. t. xxiv. f. 19. Mr. Westwood refers this insect to the modern 

 genus Dixa. (Mad. Class, ii. p. 527.) 



2 Swamra. Bibl. Nat. Ed. Hill, ii. 64. b. 3 De Geer, vi. 389. 



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