MOTIONS OF INSECTS. 



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agility can accomplish — in nearly the same manner as salmon 

 are stated to do when they wish to pass over a cateract, 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 pro- 

 duced by its mandibles may be readily heard, and the leap 

 takes place. Swammerdam 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. 1 The grub of a little 

 gnat lately noticed {Chironomus stercorarius) has a similar 

 faculty, though executed in a manner rather different. These 

 larvae, 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 man- 

 dibles, 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. 2 The grub of a fly, whose proceedings in that 

 state I have before noticed (Leptis Vermileo), will, when re- 

 moved from its habitation, endeavour to recover it by leaping. 



1 Swamm. Bibl. Nat. Ed. Hill, ii. 64. b. 2 De Geer, vi. 389. 



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