388 INSECT TRANSFORMATIONS. 



it is furnished with feet most admirably contrived for 

 taking hold of the catchweed {Galium Aparine), 

 and other trailing plants, on which it feeds. This 

 contrivance consists of cushions, formed of a slightly 

 concave mass of thick soft hair which both adheres 

 by its points, and also produces somewhat of a va- 

 cuum, which enables it to walk as easily with its head 

 perpendicularly downwards as upwards. 



The most perfect contrivance of this kind, however, 

 occurs in the domestic fly {Musca domestica), and 

 its congeners, as well as in several other insects. 

 Few can have failed to remark, that flies walk with 

 the utmost ease along the ceiling of a room, and no less 

 so upon a perpendicular looking-glass ; and though 

 this were turned downwards, the flies would not fall 

 oft', but could maintain their position undisturbed 

 with their backs hanging downwards. The conjectures 

 devised by naturalists, to account for this singular 

 circumstance, previous to the ascertaining of the 

 actual facts, are not a little amusing. " Some sup- 

 pose," says the Abbe de la Pluche, " that when the 

 fly marches over any polished body, on which neither 

 her claws nor her points can fasten, she sometimes 

 compresses her sponge and causes it to evacuate a 

 fluid, which fixes her in such a manner as prevents 

 her falling -without diminishing the facility of her 

 progress ; but it is much more probable that the 

 sponges correspond with the fleshy balls which ac- 

 company the claws of dogs and cats,* and that they 

 enable the fly to proceed with a softer pace, and con- 

 tribute to the preservation of its claws, whose pointed 

 extremities would soon be impaired without this 

 prevention. "t — " Its ability to walk on glass," says 

 S. Shaw, " proceeds partly from some little rugged- 

 ness thereon, but chiefly from a tarnish, or dirty 



* See Menageries, Lib. of Kntertaiii. Knowl. vol. i. p. 173. 

 t Spect. de la Nat. vol. i. p. 116. 



