HISTORICAL, SKETCH. xiii 



varieties are under cultivation ; and the latter process lie 

 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 tlian at present. He lays weight on wliat he calls 

 the principle of finality, " puissance mysterieuse, ind6- 

 terminee ; fatality pour les uns ; pour les autres volonte 

 providentielle, dont Taction incessante sur les ^tres vi- 

 vantes determine, a toutes les epoques de Fexistence du 

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

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

 partie. C'est cette puissance qui harmonise chaque 

 membre a Fensemble, en Tappropriant a la fonction qu'il 

 doit remplir dans Torganisme 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. Geolog.," 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 alfected by circumambient molecules of a 

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



In this same year, 1853, 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 

 fcAV have become modified. The distinction of species he 

 explains by the destruction of intermediate graduated 



*Fiom references in Bronn's " Untersuchungen ilber die Ent- 

 wickeluiigs-Gesetze," it appears that the celebrated bot-anist and 

 palaeontologist Unger published, in 1852, his belief that species 

 undergo development and modification. Balton, 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 by 

 Oken in his my?;tical "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 ^)ecial branches of natural 

 kistory or geology. 



