628 UNITY OF DESIGN. 



of attention, I shall here briefly state them ; but 

 in so doing I shall beg to premise the caution 

 that these views should for the present be re- 

 garded as hypothetical, and as by no means pos- 

 sessing the certainty of philosophical generali- 

 zations. 



The hypothesis in question is countenanced, 

 in the first place, by the supposed constancy 

 with which, in all the animals belonging to the 

 same natural group, we meet with the same con- 

 stituent elements of structure, in each respective 

 system of organs, notwithstanding the utmost 

 diversity which may exist in the forms of the 

 organs, and in the uses to which they are ap- 

 plied. This principle has been most strikingly 

 exemplified in the osteology of vertebrated ani- 

 mals ; but its truth is also inferred from the 

 examination of the mechanical fabric of Insects, 

 Crustacea, and Arachnida ; and it appears to 

 extend also to the structures subservient to other 

 functions, and particularly those of the nervous 

 system. Thus Nature has provided for the 

 locomotion of the serpent, not by the creation 

 of new structures, foreign to the type of the 

 vertebrata, but by employing the ribs in this 

 new office ; and in giving wings to a lizard, 

 she has extended these same bones to serve as 

 supjiorts to the superadded parts. In arming 

 the elephant with tusks, she has merely caused 

 two of the teeth in the upper jaw to be developed 



