to the simple straightforward language of
Lamarck.

"Long continued disuse," he writes, "in consequence of the habits which
an animal has contracted, gradually reduces an organ, and leads to its
final disappearance....

"Eyes placed in the head form an essential part of that plan on which we
observe all vertebrate organisms to be constructed. Nevertheless the
mole which uses its vision very little, has eyes which are only very
small and hardly apparent.

"The _aspalax_ of Olivier, which lives underground like the mole, and
exposes itself even less than the mole to the light of day, has wholly
lost the use of its sight, nor does it retain more than mere traces of
visual organs, these traces again being hidden under the skin and under
certain other parts which cover them up and leave not even the smallest
access to the light. The Proteus, an aquatic reptile akin to the
Salamander and living in deep and obscure cavities under water, has,
like the aspalax, no longer anything but traces of eyes
remaining--traces which are again entirely hidden and covered up.[373]

"The following consideration should be decisive.

"Light cannot penetrate everywhere, and as a consequence, animals which
live habitually in places which it cannot reach, do not have an
opportunity of using eyes, even though they have got them; but animals
which form part of a system of organization which comprises eyes as an
invariable rule among its organs, must have had eyes originally. Since
then we find among these animals some which have lost their eyes, and
which have only concealed traces of these organs, it is evident that the
impoverishment, and even disappearance of the organs in question, must
be the effect of long-continued disuse.

"A proof of this is to be found in the fact that the organ of hearing is
never in like case with that of sight; we always find it in animals of
whose system of organization hearing is a component part; and for the
following reason, namely, that sound, which is the effect of vibration
upon the ear, can penetrate everywhere, and pass even through massive
intermediate bodies. Any animal, therefore, with an organic system of
which the ear is an essential part, can always find a use for its ears,
no matter where it inhabits. We never, therefore, come upon rudimentary
ears among the vertebrata, and when, going down the scale of life lower
than the vertebrata, we come to a point at which the ear is no longer to
be found; w