VIH INTRODUCTORY. 



adaptation of the muscles and bones for the performance of 

 this most ordinary action of life, would require a volume. The 

 process is scarcely less complex in insects. Lyonnet found 

 3,993 muscles in a caterpillar, and while a large proportion be- 

 long to the internal organs, over a thousand assist in locomotion. 

 Hence the muscular power of insects is enormous. A flea will 

 leap two hundred times its own height, and cer- 

 tain large, solid beetles will move enormous 

 weights as compared to the bulk of their bodies. 

 In walking, as seen in the accompanying figure 

 (Fig. 8), three legs are thrown forward at a time, 

 two on one side and one on the other. 



Flies and many other insects can walk upside 

 down, or on glass, as easily as on a level surface. 

 8. Larva of a bee- A fly's foot, as in most other insects, consists of 

 18)< five joints (tarsal joints), to the last one of which 

 is appended a pair of stout claws, beneath which is a flat, soft, 

 fleshy cushion or pad, split into two (sometimes three) flaps, 

 beset on the under surface with fine hairs. A part of these 

 hairs are swollen at the end, which is covered with " an elastic 

 membranous expansion, capable of close contact with a highly 

 polished surface, from which a minute quantity of a clear, trans- 

 parent fluid is emitted when the fly is actively moving." (T. 

 West.) These hairs are hence called holding, or tenent, hairs. 

 With the aid of these, but mainly, as Mr. West insists, by the 

 pressure of the atmosphere, a fly is enabled to adhere to per- 

 fectly smooth surfaces. His studies show the following curious 

 facts. " That atmospheric pressure, if the area of the flaps be 

 alone considered, is equal to just one-half the weight of a fly. 

 If the area covered by the tenent hairs be added, an increase 

 of pressure is gained, equal to about one- fourth the weight of 

 a fly. This leaves one-fourth to be accounted for by slight 

 viscidity of the fluid, by the action I have so often alluded to, 

 which may be called 'grasping,' by molecular attraction, and, 



