CHELONIAN REPTILES. 465 



costal appendices, which become ossified. Thus 

 no new element has been created ; but advantage 

 has been taken of those already existing in the 

 general type of the vertebrata, to modify their 



forms, by giving them different degrees of relative 

 developement, and converting them, by these 

 transformations, into a mechanism of a very dif- 

 ferent kind, and subservient to other objects 

 than those to which they are usually applied. 

 It is scarcely possible to have stronger proofs, if 

 such were wanting, of the unity of plan which 

 has regulated the formation of all animal striic- 



VOL. I. H H 



