derstanding, its origin and that of
ideas. The following additions relative to chapters vii. and viii. of
the first part of this work are from vol. ii., pp. 451-466.

In the last of June, 1809, the menagerie of the Museum of Natural
History having received a Phoca (_Phoca vitulina_), Lamarck, as he says,
had the opportunity of observing its movements and habits. After
describing its habits in swimming and moving on land and observing its
relation to the clawed mammals, he says his main object is to remark
that the seals do not have the hind legs arranged in the same direction
as the axis of their body, because these animals are constrained to
habitually use them to form a caudal fin, closing and widening, by
spreading their digits, the paddle (_palette_) which results from their
union.

"The morses, on the contrary, which are accustomed to feed on grass
near the shore, never use their hind feet as a caudal fin; but their
feet are united together with the tail, and cannot separate. Thus in
animals of similar origin we see a new proof of the effect of habits
on the form and structure of organs."

He then turns to the flying mammals, such as the flying squirrel
(_Sciurus volans_, _aerobates_, _petaurista_, _sagitta_, and
_volucella_), and then explains the origin of their adaptation for
flying leaps.

"These animals, more modern than the seals, having the habit of
extending their limbs while leaping to form a sort of _parachute_,
can _only_ make a very prolonged leap when they glide down from a
tree or spring only a short distance from one tree to another. Now,
by frequent repetitions of such leaps, in the individuals of these
races the skin of their sides is expanded on each side into a loose
membrane, which connects the hind and fore legs, and which,
enclosing a volume of air, prevents their sudden falling. These
animals are, moreover, without membranes between the fingers and
toes.

"The Galeopithecus (_Lemur volans_), undoubtedly a more ancient form
but with the same habits as the flying squirrel (_Pteromys Geoff._),
has the skin of the _flancs_ more ample, still more developed,
connecting not only the hinder with the fore legs, but in addition
the fingers and the tail with the hind feet. Moreover, they leap
much farther than the flying squirrels, and even make a sort of
flight.[189]

"Finally, the different bats are probably mammals still older than
the Galeopit