522 MAMMALIA. 



femoral membrane ; but it never reaches the toes of the feet, 

 which are short, aud have nails. 



It is owing to this membranous sail that Bats direct their 

 course through the air in the same manner as Birds. "When they 

 are at rest, they fold their wings around them, enveloping their 

 bodies as if in a mantle, similar to our closing an umbrella to 

 diminish its volume when it is no longer required. This com- 

 parison is still more exact when we observe that the long filiform 

 digits of the animal perfectly correspond to the ribs or rods of the 

 umbrella. 



After what has been said, it will be understood that Bats are 

 not adapted for terrestrial locomotion. Their movements have 

 been observed, and the following has been remarked. When 

 they wish to move on the ground, they project as far as 

 possible the hooked nail that terminates one of their thumbs, 

 and implant it in the ground ; then, exercising a degree of 

 traction of this point, it draws the body forward in the same 

 direction by the play of the arm muscles, at the same time the 

 posterior limbs act from behind, to aid this movement. The 

 other thumb then executes the same manoeuvre, and the body 

 advances at the same rate, but no longer in the same direction. 

 It is easy to see that the creature is carried now to the right, then 

 to the left, according as it fixes itself on one or other of its thumbs, 

 and in this way the Bat walks, not in a straight line, but in a 

 series of zigzags, in which the axis of the animal represents the 

 real direction. 



An English naturalist. White, who had studied Bats in cap- 

 tivity, wrote in. error against the common opinion that they only 

 moved on the ground with much difiicult}\ He stated that, on 

 the contrary, they could run with considerable rapidity. Despite 

 this aflirmation, Ave refuse to believe in the agility of the Cheirop- 

 tera, and to look upon them as walking Mammals ; therefore we 

 think that there is exaggeration in the statement of the English 

 naturalist. 



It is certain that Bats do not descend to the ground under 

 ordinary circumstances. Besides the reason we have already 

 given for this, there is another, which is that when placed on 

 the ground they find themselves in a very inconvenient position 

 to resume their flight. Their case is then almost the same as 



