LAMARCK'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 ih.e fcetus 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 {Myrmecophagd) 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 Aspalax of Olivier {Voyage en Egypte et en 

 Perse, ii. pi. 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 



