FEET OF INSECTS. 



681 



walking over smooth surfaces in opposition to the force of gravity ; 

 yet there is still considerable uncertainty as to the precise mode 

 in which it ministers to this faculty. Some believe that the 

 Pulvilli act as suckers, the Insect being held -up by the pressure 

 of the air against their upper surface, when a vacuum is formed 

 beneath ; whilst others maintain that the adhesion is the result 

 of the secretion of a viscid liquid from the under side of the 

 foot. The careful observations of Mr. Hepworth have led him 

 to a conclusion which seems in harmony with all the facts of the 

 case ; namely, that the minute disks at the extremity of the indi- 

 vidual hairs act as suckers, and that each of them secretes a liquid 

 which, though not viscid, serves to make its adhesion perfect.* 

 And this view of the case derives confirmation from the presence of 

 a similar apparatus, on a far larger scale, on the foot of the Dytis- 

 cus (Fig. 351, a). The first joints of the Tarsus of this Insect 



Fig. 351. 



A, Foot of Bytiscv.s, showing its apparatus of Suckers ; a, h, 

 large Suckers ; c, ordinary Suckers :— B, one of the ordinary 

 Suckers more highly magnified. 



are widely expanded, so as to form a nearly-circular plate ; and 

 this is provided with a very remarkable apparatus of Suckers, of 



* See Mr. Hepworth' s communications to the " Quart. Journ. of 

 Microsc. Science," Vol. ii. (1854), p. 158, and Vol. iii. (1855), p. 312. See 

 also Mr. Tuffen West's Memoir ' On the Foot of the Fly,' in " Transact, 

 of Linn. Society," Vol. xxii., p. 393. 



