Influence of circumstances on the Actions of Animals. 971 
Vertebrate animals, of which the plan of organization is nearly 
the same, although they show much diversity in their parts, have, 
usually, their jaws armed with teeth. Nevertheless those among 
them which circumstances have given the habit of swallowing their 
food without previous mastication have been found to display a 
repressed development of these parts—that these teeth have even 
remained hidden between the osseous plates of the jaws without 
being able to appear, or all traces of them have entirely disap- 
peared. Among whales, which people have believed completely 
deprived of teeth, M. Geoffroy has found them hidden in the jaws 
of the foetus. This professor has also found in birds the groove 
where teeth should have been placed, but nothing more has been 
seen, In the class Mammalia, which embraces the most perfect 
animals, and principally those of which the plan of organization 
of the vertebr is most completely executed, not only the whale 
has no teeth for its use, but one finds also in the same condition the 
ant-eater (Myrmecophaga), in which the habit of not masticating its 
food has been introduced and preserved for a long time in its race 
Eyes in the head is the rule for a great number of diverse animals, 
and are essential to the plan of the organization of vertebrates. 
Nevertheless the mole, which by its habits has very little occasion 
to see, has only very small eyes, and which scarcely show, because 
it exercises this organ very little. 
“ The Spalax d’Olivier ” (Voyage en Egypt et en Persia, II., pl. 
82, f. 2), which lives under ground like a mole, and which is probably 
less exposed to the light of day, and has totally lost the function of 
sight, shows scarcely the rudiments of the organ which is its seat, 
and these vestiges are entirely hidden under the skin and under 
whatever other parts which cover it, which allow no access ot 
light. The Proteus, an aquatic reptile, cousin of the salamander, by 
all accounts lives in deep and obscure caverns, which are under 
ground, has, like the Spalax, only the traces of the organ of sight, 
which are covered and hidden in the same manner. Behold 
one decisive consideration relative to the question which I now 
discuss, Light does not penetrate everywhere, consequently animals 
which live habitually in those places where it does not come, lack 
occasion to exercise the organ of sight, if nature has provided them 
with it, Now, animals which partake in a ‘plan of organization 
