S74- MOTIONS OF INSECTS. 



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 ^. The other descriptions of 

 hots, 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 '^. 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 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 loco- 

 motion, have the margin of their body fringed with a 

 double row of short spines'^, which are, doubtless, use- 

 ful in the same way. 



The next order of walkers amongst apodous larva3 

 are those that move by means of fleshy tuberculiform or 

 pediform prominences, — which last resemble the spuri- 

 ous legs of the caterpillars of most Lepidoptera. Some, 

 a kind of monopods, have only one of such pi'ominences, 

 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 {CJnronojnus 



^ Rcauni. iv, 41G. /. xxxvi./. 5. Comp. Clark On the Bots, &c. 48, 



^ 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. Reauni. iv. 556. t. xxxv./. 11, 13, 15. I also observed them 



myself in the same grub. 



' See above, p. 320. '• Plate XIX. Fig. 11. 



