40 MEMOIR OF LAMARCK. 



s plastic virtue,' and other phantoms of the middle 



" It is evident, that if some well authenticated 

 facts could have heen adduced to establish one com- 

 plete step in the process of transformation, such as 

 the appearance in individuals descending from a 

 common stock, of a sense or organ entirely new, 

 and a complete disappearance of some other en- 

 joyed by their progenitors, that time alone might 

 then be supposed sufficient to bring about any 

 amount of metamorphosis. The gratuitous assump- 

 tion, therefore, of a point so vital to the theory of 

 transmutation, was unpardonable on the part of its 

 advocate*." 



The transmutability of species is a point which 

 has been maintained by many naturalists besides 

 Lamarck, and the reasons they have adduced in 

 support of their opinions are so various, that the 

 full consideration of them would be inconsistent 

 with our present purpose. It may be assumed as 

 capable of most satisfactory proof, that the muta- 

 tions which species undergo in accommodating them- 

 selves to a change of external circumstances, have a 

 definite limit, and are regulated by constant laws ; 

 and that the capability of so varying, forms part of 

 the specific character. Indefinite divergence from 

 the original type is guarded against, in the case of 

 intermixture of distinct species, by the sterility of 

 the mule offspring ; circumstances which show that 



* Principles of Geology, ii. p. 8. 



