[3] From references in Bronn’s “Untersuchungen über die Entwickelungs-Gesetze”, it appears that the celebrated botanist and palæontologist Unger published, 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 by Oken in his mystical “Natur-Philosophie”. From other references in Godron’s work “Sur l’Espèce”, 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. In 1853 a celebrated geologist, Count Keyserling (“Bulletin de la Soc. Geolog.”, 2nd Ser., tom. x, page 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 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”, &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 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 Géograph.” Bot. tom. i, page 250), “On voit que nos recherches sur la fixité ou la variation de l’espéce, nous conduisent directement aux idées émises par deux hommes justement célèbres, 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 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” 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.