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HISTORICAL SKETCH. Xlll 



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

 letin de la Soc. Geolog.," 2d 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 chemi- 

 cally affected by circumambient molecules of a particular 

 nature, and thus have given rise to new forms. 



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

 Bxcellent pamphlet ("Verhand. des Naturhist. Vereins der 

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

 opment 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 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 l'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 Rev. 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 intro- 

 duction of new species is " a regular, not a casual phenom- 

 enon," 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 " contains papers, read July 1, 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, toward whom all zoologists feel so profound a 

 respect, expressed about the year 1859 (see Prof. Rudolph 

 Wagner, " Zoologisch-Anthropologische Untersuchungen," 

 1861, s. 51) his conviction, chiefly grounded on the laws of 

 geographical distribution, that forms now perfectly distinct 

 have descended fruux a single parent-form. 



