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WHAT ARE BATS?
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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 reptiles; 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 (Rhacophorus), 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 surface 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-
