UNITY OF DESIGN. 503 



system. Thus nature has provided for the loco- 

 motion 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 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 developed 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, arrange themselves, more or less, into cer- 

 tain 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 addi- 

 tional extension of its faculties and endowments by 

 the graduated developement of elements, which 

 existed in a latent form in the primeval germ, and 

 which are evolved, in succession, as nature ad- 

 vances in her course. Thus we find that each new 

 form which arises, in following the ascending scale 

 of creation, retains a strong affinity to that which 

 had preceded it, and also tends to impress its own 

 features on those which immediately succeed ; and 

 thus their specific differences result merely from 

 the difll'erent extent and direction given to these 

 organic developements ; those of inferior races pro- 

 ceeding to a certain point only, and there stopping ; 

 while in beings of a higher rank they advance 

 farther, and lead to all the observed diversities of 

 conformation and endowments. 



