334 THE MECHANICAL FUNCTIONS. 



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the last joint of the foot, immediately between 

 the claws. On the under surface of the first 

 joint are three pair of globular cushions, and 

 another pair under the second joint. Fig. 155 

 shows these parts. The cushions are filled 

 ^s ith an elastic fibrous substance ; which, in 

 order to increase the elasticity of the whole 

 structure, is looser in its texture towards the 

 circumference. * 



The mode in which these suckers operate 

 may be distinctly seen, by observing with a 

 magnifying glass the actions of a large blue- 

 bottle fly in the inside of a glass tumbler. A 

 fly will, by the application of this apparatus, 

 remain suspended from the ceiling for any 

 length of time without the least exertion ; for 

 the weight of the body pulling against the 

 suckers serves but to strengthen their adhesion : 

 hence we find flies preferring the ceiling to the 

 floor, as a place of rest. 



Insects which, like the gnat, walk much upon 

 the surface of water, have at the ends of their feet 

 a brush of fine hair, the dry points of whicli 

 appear to repel the fluid, and prevent the leg 

 from being wetted. If these brushes be moist- 

 ened with spirit of wine, this apparent repulsion 

 no longer takes place ; and the insect imme- 

 diately sinks and is drowned. 



* Philosophical Transaction? for 1826, p. 324. 



