38 COMPAEISONS OF STRUCTURE IN ANIMALS. 



membranous wings is extreme; they are ca- 

 pable of appreciating the vibrations of the 

 atmosphere, its currents, its quiescence, and its 

 more subtile conditions, with such refined 

 nicety, that if the animal's eyes be covered up, 

 it will direct its course, avoiding every ob- 

 stacle in its way with the most surprising 

 address. The thumb of the bat is short and 

 free, and armed, as are the hind toes, with 

 a hooked claw, enabling the creature to climb 

 and shuffle itself along. 



How diiferent the structure of these mem- 

 branous organs of flight from the stout, short, 

 spade-like paws of the burrowing mole; and 

 how wisely has Providence assigned to each 

 creature that modification of structure which 

 is in due accordance Avith its instincts! The 

 very form of the mole shows it to be a bur- 

 rower; it lives, it real's its young, and pursues 

 its prey under ground, only occasionally visiting 

 tlie surface; it works out its mines and gal- 

 leries with marvellous ease and celerity, ex- 

 tending them in various directions in quest 

 of worms, which constitute its principal food. 

 If we look at its fore-paws we are at once 

 struck with their strength ^ breadth, and 

 solidity; the fingers are short and thick, com- 



