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 Tipularie 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 (Z'yrophaga 
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- 
merdam saw one, whose length did not exceed the fourth part of an inch, 
Jump in this manner out ofa 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? The grub of a little gnat lately 
noticed (Chironomus stercorarius) has a similar faculty, though executed in 
amanner rather different. These larvee, 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.8 The grub of a fly, whose proceedings in 
1 De Geer, vi. 380. t. xxiv. f, 1—9. Mr. Westwood refers this insect to the modern 
Senus Diva, (Mod. Class. ii. p. 527.) 
® Swainm, Bibl. Nat. Ed. Hill, ii, 64. b. 5 De Geer, vi. 389. 
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