Now look at the Galeopithecus or flying lemur, which formerly was
falsely ranked amongst bats. It has an extremely wide flank-membrane,
stretching from the corners of the jaw to the tail, and including the
limbs and the elongated fingers: the flank membrane is, also,
furnished with an extensor muscle. Although no graduated links of
structure, fitted for gliding through the air, now connect the
Galeopithecus with the other Lemuridae, yet I can see no difficulty in
supposing that such links formerly existed, and that each had been
formed by the same steps as in the case of the less perfectly gliding
squirrels; and that each grade of structure had been useful to its
possessor. Nor can I see any insuperable difficulty in further
believing it possible that the membrane-connected fingers and fore-arm
of the Galeopithecus might be greatly lengthened by natural selection;
and this, as far as the organs of flight are concerned, would convert
it into a bat. In bats which have the wing-membrane extended from the
top of the shoulder to the tail, including the hind-legs, we perhaps
see traces of an apparatus originally constructed for gliding through
the air rather than for flight.
If about a dozen genera of birds had become extinct or were unknown,
who would have ventured to have surmised that birds might have existed
which used their wings solely as flappers, like the logger-headed duck
(Micropterus of Eyton); as fins in the water and front legs on the
land, like the penguin; as sails, like the ostrich; and functionally
for no purpose, like the Apteryx.
Pages:
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227