242 THE MECHANICAL FUNCTIONS. 



the moist earth through which it moves, and with a form of 

 body enabling it to penetrate with least resistance the oppo- 

 sing medium. By being endowed with the power of moving 

 as easily in a backward as in a forward direction^ it is ena- 

 bled quickly to retreat in the narrow channel it has exca- 

 vated: and as a safeguard in these retrograde movements, it is 

 provided with a pair of posterior appendages, which are sup- 

 plied with large nerves, and may be regarded as serving the 

 purpose of caudal antennse. 



The fore-legs, (one of which is represented in Fig. 158"^) 

 are the burrowing implements, and they are admirably cal- 

 158* .^^-^^^^^^ culated for their peculiar ofiice, 



% ^ both in the shape and in the 

 '-.^^ mode of articulation of their 

 several divisions, which bear a 

 considerable analogy to the 

 corresponding member of the mole. Dr. Kidd observes, 

 that, compared with the other legs, and with the general size 

 of the animal, they are as if the brawny hand and arm of a 

 robust dwarf were set on the body of a delicate infant; and 

 the indications of strength which their structure manifests, 

 fully answer to their extraordinary size. For a more par- 

 ticular description of the mechanism of this instrument I 

 must refer the reader to the paper above quoted. 



§ 9. Flight of Insects. 



If the excellence of a mechanic art be measured by the 

 difficulties to be surmounted in the attainment of its object, 

 none surely would rank higher than that which has accom- 

 plished the flight of a living animal. No human skill has 

 yet contrived the construction of an automaton, capable, by 

 the operation of an internal force, of sustaining itself in the 

 air in opposition to gravity, for even a few minutes; and 

 far less of performing in that element the evolutions which 

 we daily witness even in the lowest of the insect tribes. 

 To the ultimate attainment of this faculty it would appear 

 that all the transformations they undergo in external appear- 



