MOTIONS OF INSECTS. 275 



the head, but even within the segments behind it^ ; but 

 when it is moving they are protruded, and lay hold of 

 the surface on which it is placed. They were long 

 ago noticed by the accurate Ray. " This blackness in 

 the head," says he, speaking of the maggot of the com- 

 mon flesh-fly, " is caused by two black spines or hooks, 

 which when in motion it puts forth, and fixing them 

 in the ground, so drags along its body''." — The larvaB 

 of the aphidivorous flies (Sj/iyhus, F.), the ravages of 

 which amongst the Aphides I have before described to 

 you*^, transport themselves from place to place in the 

 same way, walking by means of their teeth. Fixing 

 their hind part to the substance on which they are 

 moving, they give their body its greatest possible ten- 

 sion ; and, if I may so speak, thus take as long a step 

 as they can : next, laying hold of it with their mandi- 

 bles, by setting free the tail and relaxing the tension, 

 the former is brought near the head. Thus the animal 

 proceeds, and thus will even walk upon glass ''. Some 

 grubs, as the lesser house-fly {Musca domestica minor, 

 De Geer), have only one of these claw-teeth ; and in 

 some they have the form as well as the office of legs®. 

 Bonnet mentions an apodous larva, that, before it can 

 use its mandibles, is obliged to spin, at certain intervals, 

 little hillocks or steps of silk ; of which it then lays 

 hold by them, and so drags itself along. 



Besides their mandibular hooks, some of these grubs 



* De Geer, vi. 65. " Hist. Ins. 270. * Vol. I. 2d Ed. 264. 

 " Reaumur, iii. 369. 



' Vol. I. 2d Ed. 138. De Geer, vi. 76. Reraiaiur, iv. 376. Swamm. 

 Bibl Sut. Ed. Hill, ii. 46. a. t. xxxix. /. 3. kh. 



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