66 MECHANICAL FUNCTIONS. 



180. Doubts concerning this Mechanism. Notwith- 

 standing it would thus appear, that there could be no doubt 

 with respect to the manner in which flies are enabled to ad- 

 here to smooth surfaces, yet some entomologists still doubt 

 whether the feet of these insects really contain any organs 

 which adhere by suction. If flies adhere by the pressure 

 of the atmosphere, then, if the atmosphere be removed, it 

 is said, they would be unable to walk on a smooth, per- 

 pendicular surface. To demonstrate this, house-flies were 

 put into the glass receiver of an air-pump, and the air 

 exhausted, when it is said, " it was demonstrated to the 

 entire satisfaction of several intelligent gentlemen present, 

 that the house-fly, while it retains its vital powers unim- 

 paired, cannot only traverse the upright sides, but even 

 the interior of the dome of an exhausted receiver, and 

 that the cause of its relaxing its hold, and ultimately 

 falling from the station it occupied, was a diminution of 

 muscular force, attributable to impeded respiration." In 

 consequence of such experiments, it has been proposed to 

 account for the phenomena observed, by the secretion of 

 an adhesive matter with which the foot of the fly, or the 

 hairs on it are imbued. The advocates for this mode say, 

 that they have facts on this subject, which are quite in- 

 explicable, except on the supposition that an adhesive 

 secretion is emitted by the instruments employed in climb- 

 ing. We are, however, rather inclined to the belief that 

 these insects adhere by the pressure of the atmosphere, 

 as was so clearly shown by the observations of Sir E. 

 Home. 



INGENUITY OF INSECTS. 



181. There are some traits in the characters and habits 

 of certain insects, which appear so much like the cun- 

 ning ingenuity, and contrivance of the higher order of 

 animals, that we cannot see why they have not an equn! 



What experiment seems to make it doubtful whether flies adhere \,y i he- 

 pressure of the atmosphere? What is the conclusion of the author with 

 respect to the means by which flies adhere to smooth surfaces ? What is 

 meant by the ingenuity of insects ? 



