224 



MOTIONS OF INSECTS. 



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 

 necessary 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 

 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 backwards that 

 it employs the second. 1 The other descriptions of bots, not 

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

 with the mandibles in question, by Avhich 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.' 2 Other larvas 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 mentioned 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 locomotion, 

 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 



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



2 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. 11. 13. 15. I also observed them myself in the same grub. 



