308 LAMARCK, HIS LIFE AND WORK 
power of sight; also it possesses only vestiges of the 
organ of which it is the seat; and yet these vestiges 
are wholly concealed under the skin and other parts 
which cover them, and do not permit the least access 
to the light. 
“The Proteus, an aquatic reptile allied to the sala- 
mander in its structure, and which lives in the dark 
subterranean waters of deep caves, has, like the As- 
palax, only vestiges of the organs of sight—vestiges 
which are covered and concealed in the same manner. 
““We turn to a decisive consideration relative to 
this question. 
“Light does not penetrate everywhere; conse- 
quently animals which habitually live in situations 
where it does not penetrate lack the occasion of 
exercising the organs of sight, if nature has provided 
them with them. Moreover, the animals which make 
part of the plan of organization in which eyes are 
necessarily present, have originally had them. How- 
ever, since we find them among those which are de- 
prived of the use of this organ, and which have only 
vestiges concealed and covered over, it should be 
evident that the impoverishment and even the dis- 
appearance of these organs are the result of a con- 
stant lack of exercise. 
“What proves it is that the organ of hearing is 
never in this condition, and that we always find it in 
the animals when the nature of their organization 
should require its existence; the reason is as follows, 
“The cause of sound, that which, moved by the 
shock or the vibrations of bodies, transmits to the 
organ of hearing the impression which it receives, 
penetrates everywhere, traverses all the media, and 
even the mass of the densest bodies: from this it re- 
sults that every animal which makes a part of a plan 
of organization to which hearzng is essential, has 
always occasion to exercise this organ in whatever 
situation it lives. So, among the vertebrate animals 
