326 FROM THE GREEKS TO DARWIN 



advance in the knowledge of the different organized 

 bodies which cover the surface of the globe, the more 

 our embarrassment increases, to determine what 

 ought to be regarded as a species, and still more how 

 to limit and distinguish genera. . . . 



Although important changes in the nature of the 

 places which they inhabit modify the organization 

 of animals as well as vegetables, yet the former, says 

 Lamarck, require more time to complete a consider- 

 able degree of transmutation, and, consequently, we 

 are less sensible of such occurrences. Next to a di- 

 versity of the medium in which animals or plants may 

 live, the circumstances which have most influence in 

 modifying their organs are differences in exposure, 

 climate, the nature of the soil, and other local par- 

 ticulars. These circumstances are as varied as are 

 the characters of species, and, like them, pass by 

 insensible shades into each other, there being every 

 intermediate gradation between the opposite ex- 

 tremes. . . . 



The theory of the transmutation of species . . . 

 has met with some degree of favour from many natu- 

 ralists, from their desire to dispense, as far as pos- 

 sible, with the repeated intervention of a First Cause, 

 as often as geological monuments attest the succes- 

 sive appearance of new races of animals and plants, 

 and the extinction of those pre-existing. . . . 



If we look for some of those essential changes 

 which would be required to lend even the semblance 

 of a foundation for the theory of Lamarck, respect- 

 ing the growi:h of new organs and the gradual oblit- 

 eration of others, we find nothing of the kind. . . . 



