DAMARGE S LABOR V” OF VDE SCENT, 309 
we see none deprived of their organs of hearing; but 
in the groups below them, when the same organs are 
once wanting, we do not again find them. 
“It is not so with the organ of sight, for we see 
this organ disappear, reappear, and again disappear, 
in proportion to the possibility or impossibility of 
the animal’s exercising it. 
“In the acephalous molluscs, the great development 
of the mantle of these molluscs has rendered their 
eyes and even their head entirely useless. These 
organs, also forming a part of a plan of organization 
which should comprise them, have disappeared and 
atrophied from constant lack of use. 
“Finally, it isa part of the plan of organization of 
reptiles, as in other vertebrate animals, to have four 
legs appended to their skeleton. The serpents should 
consequently have four, though they do not form the 
lowest order of reptiles, and are not so near the fishes 
as the batrachians (the frogs, the salamanders, etc.). 
‘¢ However, the serpents having taken up the habit 
of gliding along the ground, and of concealing them- 
selves in the grass, their body, owing to continu- 
ally repeated efforts to elongate itself so as to pass 
through narrow spaces, has acquired a considerable 
length disproportionate to its size. Moreover, limbs 
would have been very useless to these animals, and 
consequently would not have been employed: because 
long legs would have interfered with their need of 
gliding, and very short legs, not being more than four 
in number, would have been incapable of moving 
their body. Hence the lack of use of these parts 
having been constant in the races of these animals, 
has caused the total disappearance of these same 
parts, although really included in the plan of organi- 
zation of the animals of their class. 
““Many insects which by the natural character of 
their order, and even of their genus, should have 
wings, lack them more or less completely from dis- 
