322 MOTIONS OF INSECTS. 



The instruments by which a fly effects this purpose 

 are two suckers connected with the last joint of the tar- 

 sus by a narrow infundibular neck, which has power of 

 motion in all directions, immediately under the root of 

 each claw. These suckers consist of a membrane ca- 

 pable of extension and contraction ; they are concavo- 

 convex with serrated edges, the concave surface being 

 downy, and the convex granulated. When in action 

 they are separated from each other, and the membrane 

 expanded so as to increase the surface : by applying 

 this closely to the plane of position, the air is suffi- 

 ciently expelled to produce the pressure necessary to 

 keep the animal from falling. When the suckers are 

 disengaged, they are brought together again so as to be 

 confined within the space between the two claws. This 

 may be seen by looking at the movements of a fly in the 

 inside of a glass tumbler with a common microscope 8 . 

 Thus the fly you see does no more than the leech has 

 been long known to do, when moving in a glass vessel. 

 Furnished with a sucker at each extremity, by means of 

 these organs it marches up and down at its pleasure, or 

 as the state of the atmosphere inclines it. 



Dipterous insects, which in general have these or- 

 gans, and some three on each foot b , are not exclusively 

 gifted with them ; for various others in different orders 

 have them, and some in greater numbers. As I lately 

 observed, the foot-cushions of the Buprestes are some- 

 thing very like them, particularly those of B.fascicularis. 

 A Brazilian beetle in my cabinet, belonging to the 

 family of the Clerida, but not arranging well under 

 any of Latreille's genera, which I have named Priocera 

 a Philos, Trans. 1816. 325. t. xviii./. 1-7. b Ibid. / 8-11. 



