20 ESSAY ON CLASSIFICATION 



when they live in waters or upon a soil containing more or less lime- 

 stone, etc. The rapidity or slowness of the growth is also influenced 

 in a measure by the course of the seasons in different years; so is also 

 the fecundity, the duration of life, etc. But all this has nothing to 

 do with the essential characteristics of animals. 



A book has yet to be written upon the independence of organized 

 beings of physical causes, as most of what is generally ascribed to 

 the influence of physical agents upon organized beings ought to be 

 considered as a connection established between them in the general 

 plan of creation. 



SECTION IV 

 UNITY OF PLAN IN OTHERWISE HIGHLY DIVERSIFIED TYPES 



Nothing is more striking throughout the animal and vegetable 

 kingdoms than the unity of plan in the structure of the most diver- 

 sified types. From pole to pole, in every longitude, mammalia, birds, 

 reptiles, and fishes exhibit one and the same plan of structure, in- 

 volving abstract conceptions of the highest order, far transcending 

 the broadest generalizations of man, for it is only after the most 

 laborious investigations man has arrived at an imperfect understand- 

 ing of this plan. Other plans, equally wonderful, may be traced in 

 Articulata, in Mollusks, in Radiata,-^ and in the various types of 

 plants. And yet the logical connection, these beautiful harmonies, 

 this infinite diversity in unity are represented by some as the result 

 of forces exhibiting no trace of intelligence, no power of thinking, 

 no faculty of combination, no knowledge of time and space. If there 

 is anything which places man above all other beings in nature, it is 

 precisely the circumstance that he possesses those noble attributes 

 without which, in their most exalted excellence and perfection, not 

 one of these general traits of relationship so characteristic of the 

 great types of the animal and vegetable kingdoms can be understood 

 or even perceived. How, then, could these relations have been de- 

 vised without similar powers? If all these relations are almost beyond 



^Agassiz, Twelve Lectures on Comparative Embryology (Boston, 1849); "On Animal 

 Morphology." Proceedings, AAAS, II (1850), 411-423. 



