18 GENERAL PRINCIPLES OF ZOOLOGY 



developing his conception of the orgin of species, the fundamental ideas 

 of which he communicated to friends, but not until 1858 did Darwin 

 decide to make them public. In this year he received an essay by Wallace 

 which in its most important points coincided with his own views. At the 

 same time with Wallace's manuscript an abstract of Darwin's theory was 

 published. In the next year (1859) appeared the most important of his 

 writings, "On the Origin of Species by means of Natural Selection," and 

 in rapid succession a splendid series of works, the most important of 

 which are: (i) " Upon the Variation of Plants and Animals under Domes- 

 tication," (2) on "The Descent of Man." 



No scientific work of that century has attracted so much attention in 

 the whole educated world, as "The Origin of Species." It was generally 

 received as something entirely new, so completely had the scientific 

 tradition been lost. In professional circles it was stoutly combated by one 

 faction, with- another it found hesitating acceptance. Only a few men 

 placed themselves from the beginning in a decided manner on the side 

 of the great British investigator. There was a lively scientific battle, 

 which ended in a brilliant victory for the theory of evolution. At the 

 present time all our scientific thoughts are permeated with the idea of 

 evolution. 



Post-Darwinian Writers. Among the men who have most influ- 

 enced this rapid advance is to be mentioned, besides A. R. W T allace, the 

 co-founder of Darwinism, above all Ernst Haeckel, who in his "General 

 Morphology" and his "Natural History of Creation" has done much 

 towards the extension of the theory. Among other energetic defenders 

 of the theory in Germany should be mentioned Fritz Miiller, Carl Vogt, 

 Weismann, Moritz Wagner, and Nageli. Among the English naturalists 

 are to be named particularly Huxley, Hooker, and Lyell. In America 

 Gray, Cope, Morse, and Hyatt were early supporters. Darwinism was 

 long in obtaining an entrance into France. 



DARWIN'S THEORY OF THE ORIGIN OF SPECIES. 



Before Darwin wrote the idea of fixity of species prevailed. It was 

 recognized that all the individuals of a species are not alike, and that 

 more or less variability occurs, so that it was possible to distinguish races 

 and varieties within the species, but it was believed that the variations 

 never transcended specific bounds. 



Darwin begins with a criticism of the term species. Are the concep- 

 tions of species on the one side and that of race and variety on the other 

 something entirely different? Are there special criteria for determining 



