UNITY OF DESIGN. 439 



quences, by many naturalists, of the liighcst eminence, on 

 the continent. As the facts on wliicli tliis hypothesis is 

 supported, and the views wliich it unfolds, are highly de- 

 serving of attention, I sliall here briefly state them; but in 

 so doing I shall beg to premise the caution that these views 

 should, for the present, be regarded as hyj)othctical, and as 

 by no means possessing the certainty of philosophical ge- 

 neralizations. 



The hypothesis in question is countenanced, in the first 

 place, by the supposed constancy with which, in all the ani- 

 mals belonging to the same natural group, we meet with the 

 same constituent 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 applied. This jjrinciple has been most 

 strikingly exemplified in the osteology of vertcbrated ani- 

 mals; but its truth is also inferred from tlie 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 sys- 

 tem. Thus Nature has provided for the locomotion of the 

 serpent, not by the creation of new structures, foreign to 

 the type of the vertebiata, but by empIo3'ing the ribs in this 

 new office; and in giving wings to a lizard, she has extended 

 these same bones to serve as supports to the superadded 

 parts. In arming the elephant .with tusks, she has merely 

 caused two of the teeth in the upper jaw to be develojied 

 into these formidable weapons; and in providing it with an 

 instrument of prehension, has only resorted to a greater 

 elongation of the snout. 



The law of Gradation^ in conformity to which all the 

 living, together with the extinct races, of organic nature, ar- 

 range themselves more or less, into certain regular series, 

 is one of the consequences which have been deduced from 

 the hypothesis we are considering. Every fresh copy taken 

 of the original type is supposed to receive some additional 

 extension of its Jii\culties and endowments by the graduated 



