XX HISTORICAL SKETCH. 



In 1853 a celebrated geologist, Count Keyserling (' Bulletin dc 

 la Soc. Geolog.,' 2nd Ser., torn. x. p. 357), suggested 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 circum- 

 ambient molecules of a particular nature, and thus have given 

 rise to new forms. 



In this same year, 1853, Dr. Schaaffhausen published an excel- 

 lent pamphlet ('Verhand. des Naturhist. Vereins der Preuss. 

 Rheinlands,' &c.), in which he maintains the development 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 inter- 

 mediate graduated forms. " Thus living plants and animals are 

 not separated from the extinct by new creations, but are to be 

 regarded as their descendants through continued reproduction." 



A well-known French botanist, M. Lecoq, writes in 1854 

 (' Etudes sur Geograph. Bot.,' torn. i. p. 250), " On voit que nos 

 recherches sur la fixite ou la variation de 1'espece, nous conduisent 

 directement aux idees emises, par deux hommes justement celebres, 

 Geoffroy Saint-Hilaire et Goethe." Some other passages scattered 

 through M. Lecoq's large work, make it a little doubtful how far 

 he extends his views on the modification of species. 



The ' Philosophy of Creation ' has been treated in a masterly 

 manner by the Bev. Baden Powell, in his ' Essays on the Unity 

 of Worlds,' 1855. Nothing can be more striking than the manner 

 in which he shows that the introduction of new species is "a 

 regular, not a casual phenomenon," or, as Sir John Herschel 

 expresses it, "a natural in contradistinction to a miraculous 

 process." 



The third volume of the ' Journal of the Linnean Society ' con- 

 tains papers, read July 1st, 1858, by Mr. Wallace and myself, in 

 which, as stated in the introductory remarks to this volume, the 

 theory of Natural Selection is promulgated by Mr. Wallace with 

 admirable force and clearness. 



Von Baer, towards whom all zoologists feel so profound a 

 respect, expressed about the year 1859 (see Prof. Budolph Wagner, 

 ' Zoologisch-Anthropologische Untersuchungen, 5 1861, s. 51) his 

 conviction, chiefly grounded on the laws of geographical distribu- 



references in Godron's work ' Sur 1'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-four authors named in this Historical Sketch, 

 who believe in the modification of species, or at least disbelieve in separate 

 acts of creation, twenty-seven have written on special branches of natural 

 history or geology. 



