338 LAMARCK, HIS LIFE AND WORK 
(chapter vii.) is devoted to the understanding, its origin 
and that of ideas. The following additions relative 
to see vii. and viii. of the first part of this work 
e from vol. ii., pp. 451-4606. 
ec the ace of June, 1809, the menagerie of the 
Museum of Natural History having received a Phoca 
(Phoca vitulina), Lamarck, as he says, had the oppor- 
tunity of observing its movements and habits. After 
describing its habits in swimming and moving on 
land and observing its relation to the clawed mam- 
mals, 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 (falette) which results from 
their union. 
“The morses, on the contrary, which are accus- 
tomed 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 (Sczurus volans, erobates, 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 foom one tree to another. Now, by 
frequent repetitions of such leaps, in the individuals 
