370 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



sleeve and the rhachitomous vertebral column, the 

 only difference being that in the animal it is exhib- 

 ited on both sides, 



on onlv one 



This difference is, 

 of course, due to 

 the fact that the 

 animal can bend 

 himself in both di- 

 rections, while the 

 arm only bends in 

 one direction. 



It results from 

 the above obser- 

 vations that the 

 structure of the 

 rhachitomous ver- 

 tebral column has 

 been produced by 

 the movements of 



the body j rom side 



to side, as in swim- 

 ming, during the 

 process of the de- 

 posit of mineral ma- 

 terials and around 

 the chorda dorsa- 

 lis. 1 



^Njpfcf See figures 113 



- to 1140 where the 



coat-sleeve is com- 

 pared with the "rhachitomous" vertebrae of primitive 



1 See American Naturalist, January, 1884. 



