ELAMARCKE'S THEORY OF DESCENT 307 
prove it by the citation of the leading known facts 
on which it is based. 
“The vertebrate animals, whose plan of organiza- 
tion is in all nearly the same, although they offer 
much diversity in their parts, have jaws armed with. 
teeth ; moreover, those among them which circum- 
stances have placed in the habit of swallowing their 
food without previous mastication are exposed to the 
result that their teeth become undeveloped. These 
teeth, then, either remain concealed between the 
bony edges of the jaws, without appearing above, or 
even their gums are found to have been atrophied. 
“In the baleen whales, which have been supposed 
to be completely deprived of teeth, M. Geoffroy has 
found them concealed in the jaws of the fe¢us of this 
animal. This professor has also found in the birds 
the groove where the teeth should be situated; but 
they are no longer to be seen there 
“In the class even of mammals, which comprises 
the most perfect animals, and chiefly those in which 
the vertebrate plan of organization is most perfectly 
carried out, not only the baleen has no usable teeth, 
but the ant-eater (A7yrmecophaga) is also in the same 
condition, whose habit of not masticating its food has 
been for a long time established and preserved in its 
race. 
“The presence of eyes in the head is a character- 
istic of a great number of different animals, and be- 
comes an essential part of the plan of organization of 
vertebrates. 
“ Nevertheless the mole, which owing to its habits 
makes very little use of vision, has only very small 
eyes, which are scarcely visible, since they exercise 
these organs to a very slight extent. 
“The A spalax of ‘Olivier (Voyage en Egypte et en 
Perse, ii. pl. 28 f. 2), which lives under ground like the 
mole, and which probably exposes itself still less than 
that animal to the light of day, has totally lost the 
