WHAT ARE BATS? 



529 



extensive " alar membrane," but a short expansion of skin connects 

 together not only the fingers but the toes also (which is not the case 

 in bats), and has a true interfemoral membrane extending from the 

 hind-legs to the tail. 



Fig. 3. A Flying Frog. 



There is no other such instance in beasts, or in any existing rep- 

 tiles ; but web-footedness is carried to such an extreme degree in a 

 certain frog found in Borneo as to give rise to the conjecture that it 

 was a flying animal. 



Mr. Wallace, in his travels in the Malay Archipelago, encountered 

 in Borneo a tree-frog (Jthacophorus), to which he considered that the 

 term " flying " might be applied. He tells us : 



" One of the most curious and interesting creatures which I met with in 

 Borneo was a large tree-frog, which was brought me by one of the Chinese 

 workmen. He assured me that he had seen it come down in a slanting direction 

 from a high tree as if it flew. On examining it I found the toes very long and 

 fully webbed to their extremity, so that, when expanded, they offered a surface 

 much larger than the body. The fore-legs were also bordered by a membrane, 

 and the body was capable of considerable inflation. The back and limbs were of 

 a very deep, shining, green color, the under surfaco of the inner toes yellow, while 

 the webs were black rayed with yellow. The body was about four inches long, 

 while the webs of each hind-foot, when fully expanded, covered a surface of four 

 square inches, and the webs of all the feet together about twelve square inches. 

 As the extremities of the toes have dilated disks for adhesion, showing the creat- 

 vol. ix. 34 



