UNITY OF DESIGN. 627 



reproduction are effected. To specify all the 

 examples which might be adduced in confirma- 

 tion of this obvious truth is here unnecessary ; 

 for it would be only to repeat the numerous facts 

 already noticed in every chapter of this treatise, 

 relative to each natural group of living beings ; 

 and it was, indeed, chiefly by the aid of such 

 analogies, that we were enabled to connect and 

 generalize those facts. We have seen that, in 

 constructing each of the divisions so established, 

 Nature appears to have kept in view a certain 

 definite type, or ideal standard, to which, amidst 

 innumerable modifications, rendered necessary 

 by the varying circumstances and diff*erent des- 

 tinations of each species, she always shows a 

 decided tendency to conform. It would almost 

 seem as if, in laying the foundations of each or- 

 ganized fabric, she had commenced by taking 

 an exact copy of this primitive model ; and, in 

 building the superstructure, had allowed herself 

 to depart from the original plan only for the pur- 

 pose of accommodation to certain specific and 

 ulterior objects, conformably with the destina- 

 tion of that particular race of created beings. 

 Such, indeed, is the hypothetical principle, 

 which, under the title of unity of composition, 

 has been adopted, and zealously pursued in all 

 its consequences, by many naturalists of the 

 highest eminence on the continent. As the 

 facts on which this hypothesis is supported, and 

 the views which it unfolds, are highly deserving 



