434 MOTIONS OF INSECTS. 



legs by means of claws at their anus. Thus that of the flesh-fly, Ray tells 

 us in the place just quoted, pushes itself by the protruded spines of its tail. 

 The larva, also, of a long-legged gnat (Limnobia replicata), which in that 

 state lives in the water, is furnished with these anal claws, which, in con- 

 junction with its annular tension and relaxation, and the hooks of its 

 mouth, assist it in walking over the aquatic plants. 1 



A remarkable difference, according to their station, obtains in the bots 

 of gad-flies (CEstridai) ; those that are subcutaneous (Cuticolce Clark) having 

 no unguiform mandibles ; while those that are gastric (Gastricoke Clark), 

 and those that inhabit the maxillary sinuses of animals (Cavicolce Clark), 

 are furnished with them. In this we evidently see Creative Wisdom adapt- 

 ing means to their end, for the cuticular bots having no plane surface to 

 move upon, and imbibing a liquid food, in them the mandibular hooks 

 would be superfluous. But they are furnished with other means by which 

 they can accomplish such motions, and in contrary directions, as are neces- 

 sary to them ; the anterior part of each segment being beset with numbers 

 of very minute spines, not visible except under a strong magnifier, sometimes 

 arranged in bundles, which all look towards the anus ; and the posterior 

 part is, as it were, paved with similar hooks, but smaller, which point to the 

 head. Thus we may conceive, when the animal wants to move forward, 

 that it pushes itself by the first set of hooks, keeping the rest, which 

 would otherwise impede motion in that direction, pressed close to its skin, 

 or it may depress that part of the segment, and when it would move back- 

 wards that it employs the second. 2 The other descriptions of bots, not 

 being embedded in the flesh, but fixed to a plane, are armed with the 

 mandibles in question, by which they can not only suspend themselves in 

 their several stations, but likewise, with the aid of the spines with which 

 their segments also are furnished, move at their pleasure. 3 Other larvae of 

 flies, as well as the bots, are furnished with spines or hooks by which 

 they take stronger hold to assist them in their motions. Those men- 

 tioned in my last letter as inhabiting the nests of humble-bees, besides the 

 six radii that arm their anus, and which, perhaps, may assist them in loco- 

 motion, have the margin of their body fringed with a double row of short 

 spines, which are, doubtless, useful in the same way. 



The next order of walkers amongst apodous larvae are those that move 

 by means of fleshy tuberculiform or pediform prominences, which last 

 resemble the spurious legs of the caterpillars of most Lepidoptera. Some, 

 a kind of monopods, have only one of such prominences, which, being always 

 fixed almost under the head, may serve, in some degree, the purpose of an 

 unguiform mandible. The grub of a kind of gnat (Chironomus stercorarius), 

 and also another, probably of the Tipularian tribe (found by De Geer in 

 a subputrescent stalk of Angelica, which he was unable to trace to the fly), 

 have each a fleshy leg on the underside of the first segment, which points 

 towards the head and assists them in their motions. 4 Others again go a 

 little further, and are supported at their anterior extremity by a pair of 

 spurious legs. An aquatic larva of a most singular form, and of the same 



1 De Geer, vi. 355. 



2 Reaum. iv. 416. t. xxxvi. f. 5. Compare Clark On the Bots, &c. 48. 



5 Mr. Clark (ibid. 62.) observed only rough points on the bots of the sheep, but 

 these also have spines or hooks looking'towards the anus. Reaum. iv. 556. t. xxxv. 

 f. 1 1. 13. 15. I also observed them myself in the same grub. 



4 De Geer, vi. t. xxii. f. 15. i. t. xviii. f. 8. p. 



