HISTORICAL SKETCH 21 



bryos of many species undergo, from the difficulty of dis- 

 tinguishing species and varieties, and from the principle 

 of general gradation, that species have been modified; and 

 he attributes the modification to the change of circum- 

 stances. The author (1855) has also treated Psychology 

 on the principle of the necessary acquirement of each 

 mental power and capacity by gradation. 



In 1852 M. Naudin, a distinguished botanist, expressly 

 stated, in an admirable paper on the Origin of Species 

 ("Revue Horticole," page 102; since partly republished 

 in the "Nouvelles Archives du Museum," tom. i. page 

 171), his belief that species are formed in an analogous 

 manner as varieties are under cultivation; and the latter 

 process he attributes to man's power of selection. But 

 he does not show how selection acts under nature. He 

 believes, like Dean Herbert, that species, when nascent, 

 were more plastic than at present. He lays weight on 

 what he calls the principle of finality, ''puissance mys- 

 terieuse, ind^termin^e; fatality pour les uns; pour les au- 

 tres, volunt^ providentielle, dont Taction incessante sur 

 les etres vivants determine, a toutes les epoques de I'ex- 

 istence du monde, la forme, le volume, et la durde de 

 chacun d'eux, en raison de sa destine dans I'ordre de 

 choses dont il fait partie. C'est cette puissance qui har- 

 monise chaque membre a I'ensemble, en I'appropriant a 

 la fonction qu'il doit remplir dans I'organisme general 

 de la nature, fonction qui est pour lui sa raison d'etre." ' 



^ From references in Bronn's "Untersuchungen iiber die Entwickelunga- 

 Gesetze," it appears that the celebrated botanist and paleontologist Unger pub- 

 Kshed, in 1852, his belief that species undergo development and modification. 

 Dalton, likewise, in Pander and Dalton's work on Fossil Sloths, expressed, in 

 1821, a similar belief. Similar views have, as is well known, been maintained 



