HISTOBIOAL SKMTOM. xiii 



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 mysterieuse, inde- 

 termin6e ; fatalite pour les uns ; pour les autres volont6 

 providentielle, dont Faction incessante sur les ^tres vi- 

 vantes determine, k toutes les epoques de I'existence du 

 monde, la forme, le volume, et la duree de chacun d'eux, 

 en raison de sa destin6e dans Tordre de choses dont il fait 

 partie. C'est cette puissance qui harmonise chaque 

 membre a I'ensemble, en Tappropriant k la fonction qu'il 

 doit remplir dans I'organisme general de la nature, fonc- 

 tion qui est pour lui sa raison d'etre." * 



In 1853 a celebrated geologist. Count Keyserling ("Bul- 

 letin de la Soc. G^olog.," 2d Ser., tom. x, p. 357), sug- 

 gested that as new diseases, supposed to have been caused 

 by some miasma have arisen and spread over the world, so 

 at certain periods the germs of existing species may have 

 been chemically affected by circumambient molecules of a 

 particular nature, and tlms have given rise to new forms. 



In this same year, 18537 Dr. Schaaffhausen published an 

 excellent pamphlet (" Verhand. des Naturhist. Vereins der 

 Preuss. Rheinlands," etc. ), in which he maintains the de- 

 velopment of organic forms on the earth. He infers that 

 many species have kept true for long periods, whereas a 

 few have become modified. The distinction of species he 

 explains by the destruction of intermediate graduated 



*Froiii references in Bronn's " Untersucliungen iiber die Ent- 

 wickelungs-Gesetze," it appears that tlie celebrated botanist and 

 palseontologist Unger published, in 1853, his belief that species 

 undergo development and modification. Dalton, likewise, in Pander 

 and Dalton's work on Fossil Sloths, expressed, in 1831, a similar 

 belief. Similar views have, as is well known, been maintained by 

 Oken in his mystical " Natur-Philosophie. " From other references 

 in Godron's work "Sur I'Espece," it seems that Bory St. Vincent, 

 Burdach, Poiret and Fries, have all admitted that new species are 

 continually being produced. I may add, that of the thirty-fonr 

 authors named in this Historical Sketch, who believe in the modi- 

 cation of species, or at least disbelieve in separate acts of crea- 

 tion, twenty-seven have written on special branches of natural 

 history or geology. 



