5f)-2 UNITY OF DESIGN. 



conform. It would almost seem as if, in laying the 

 foundations of each organized fabric, she liad com- 

 menced 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 purpose of accommodation to certain 

 specific and ulterior objects, conformably with the 

 destination of that particular race of created beings. 

 Such, indeed, is the hypothetical principle, which, 

 under the title of unitij of composition, has been 

 adopted, and zealously pursued in all its conse- 

 quences, by many naturalists of the highest emi- 

 nence on the continent. As the facts on which 

 this hypothesis is supported, and the views which 

 it unfolds, are highly deserving 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 regarded as quite hypothetical, and 

 far from possessing the certainty of philosophical 

 generalizations. 



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 constituent 

 elements of structure, in each respective system of 

 organs ; notwithstanding the utmost diversity wliich 

 may exist in the forms of the organs, and in the 

 uses to which they are applied. This principle has 

 been most strikingly exemplified in the osteology 

 of vertebrated animals : 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 



