68 MECHANICAL FUNCTIONS. 



most easy position they can take. The Beetle tribe, 

 and the Grass-hoppers, are furnished with this appara- 

 tus. They cannot climb up smooth surfaces, as a polish- 

 ed door, or a pane of glass, their hooks being useless,, 

 without some degree of roughness. 



Some Insects walk by Atmospheric pressure. Other 

 Insects are furnished with a curious, and somewhat com- 

 plicated apparatus, by which they are enabled to walk 

 not only upon rough, but also upon the smoothest sur- 

 faces, even with their backs downwards. It is well 

 known, that the common house fly, (Musca domestica,) 

 prefers this position to all others, for the purpose of re- 

 pose. Hence we may infer, that this is the easiest po- 

 sition the Insect can take, and therefore the one which 

 requires the least muscular exertion. 



There has been much diversity of opinion among 

 naturalists, by what means, these Insects are able 

 thus to suspend themselves on surfaces entirely smooth, 

 with so much ease as to prefer this position for sleep- 

 ing. Dr. Derham in his Physico-Theology, speaking on 

 this subject, says, " that divers flies and other Insects, 

 besides their sharp hooked nails, have also skinny palms 

 to their feet, to enable them to stick on glass and other 

 smooth bodies by means of the pressure of the atmos- 

 phere, after the manner I have seen boys carry heavy 

 stones with only a wet piece of leather clapped on the 

 top of the stone." This theory acquired additional 

 weight, or rather was confirmed in the opinions of most 

 entomologists by the elaborate and celebrated experi- 

 ments of Sir Everard Home, in which he was assisted 

 by the microscopic observations, and drawings of M. 

 Bauer. 



Mr. Roget, in his Animal and Vegetable Physiology, 

 one of the most recently published " Bridgwater Trea- 

 tises," has given the following description of this curious 

 mechanism. 



Mechanism of the Foot of the house Fly. In the 

 house Fly, that part of the last joint of the tarsus, which 



Why cannot they walk on smooth surfaces 7 



