LAMARCK’S THEORY OF DESCENT 339 
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 addi- 
tion 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.* 
“Finally, the different bats are probably mam- 
mals still older than the Galeopithecus, in the habit 
of extending their membrane and even their fin- 
gers to encompass a greater volume of air, so as to 
sustain their bodies when they fly out into the air. 
“ By these habits, for so long a period contracted 
and preserved, the bats have obtained not only lateral 
membranes, but also an extraordinary elongation of 
the fingers of their fore feet (with the exception of 
the thumb), between which are these very ample 
membranes uniting them; so that these membranes 
of the hands become continuous with those of the 
* It is interesting to compare with this Darwin’s theory of the 
origin of the same animals, the flying squirrels and Galeopithecus 
(Origin of Species, 5th edition, New York, pp. 173-174), and see how 
he invokes the Lamarckian factors of change of ‘‘ climate and vege- 
tation” and ‘‘ changing conditions of life,” to originate the variations 
before natural selection can act. His account is a mixture of La- 
marckism with the added Darwinian factors of competition and 
natural selection. We agree with this view, that the change in en- 
vironment and competition sets the ball in motion, the work being 
finished by the selective process. The act of springing and the first 
attempts at flying also involve strong emotions and mental efforts, 
and it can hardly be denied that these Lamarckian factors came 
into continual play during the process of evolution of these flying 
creatures. 
