MOTIONS OP INSECTS. 277 



of the segment; — and when it would move backwards 

 that it employs the second^. 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^. 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 mo- 

 tions. 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 larvse 

 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 pro- 

 minences, 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 (Ti- 

 pula stercoraria, De Geer), and also another, probably 

 of the Tipulidan tribe (found by De Geer in a subpu- 

 trescent stalk of Angelica, M'hich he was unable to trace 



* RcaHtn. iv. 416. t. xxxvi. /. 5. Compare Clark On the Bots, &c. 4S. 



*" Mr. Clark (ibid. 62) observed only rough points on tlie bots of the 

 sheep, but these also have spines or hooks looking towards the anns, 

 Reauin. iv. 556. t. xxxv. /. 11, 13, 15. I also observed them mvself iu 

 the same grub. « See above, p. '.i'i3. 



" Plate XIX. Fig. 11. 



