WHAT ARE BATS? 
231 
(which is not the case in bats), and has a true interfemoral 
membrane extending from the hind-legs to the tail. 
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, en- 
countered 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 colour, 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 discs 
for adhesion, showing the creature to be a true tree-frog, it is 
difficult to imagine that this immense membrane of the toes 
can be for the purpose of swimming only, and the account of 
the Chinaman that it flew down from the tree becomes more 
credible.” 
Although no existing reptile is thus furnished, there is 
a small Asiatic lizard which is ordinarily spoken of as “ flying,” 
the Draco volans. And, in fact, though this creature cannot 
truly fly, but only flit, it has a membrane which can be ex- 
tended from each side of the body, and which, like the bat’s 
wing, is supported by a number of bony rods. These rods, 
however, are not, as in the bat, enormously elongated fingers, 
but are elongated ribs, which stand out freely from the body 
when jumping, but otherwise are folded back against the flanks. 
Existing reptiles, then, present us with no close resemblance 
to bat-structure ; but when we come to extinct reptiles — reptiles 
which flourished during and anterior to the deposition of our 
chalk cliffs — the secondary or mesozoic period — we there find 
reptiles to have existed which present the most striking analogies 
with existing bats in all that regards their modes of locomotion, 
and their structure as far as it is related to such modes of 
locomotion. 
