1896.] lyi [Ortmann. 



most of the successors of Darwin, especially those who pretended to 

 have modified, corrected or enlarged his views in any respect, have not 

 understood his theory correctly : generally the origin of variations, vari- 

 eties and species has been hopelessly confused, and the latter is especially 

 true of the writings of Weismann, in which the origin of species and vari- 

 eties, and the origin of the adaptive characters of life are mixed up con- 

 stantly.* 



In, conclusion I should like to add that the principle of separation, as 

 set forth above, bears very importantly on the definition of the systematic 

 term Species, and indeed, that it alone enables us to give a correct defini- 

 tion of it. There is no doubt that a proper and logical definition of any 

 term depends largely on the knowledge of the genesis of the object, and 

 in the present case we may say that if the process of the formation of 

 species is properly understood, we can derive from this knowledge a defi- 

 nition of the term species. In my book often above referred to, I have 

 propounded the following:! " W^ designate as Species such forms as in 

 consequence of separation differ sharply and constantly by morphological 

 character s from allied coexisting forms. " It is not necessary that separa- 

 tion should be still evident in all the existing species : the separating 

 causes have often disappeared, while their result, tlie difterent species, 

 still exist. But then the separation in the past must have been sufiicient 

 to modify and difi"erentiate the respective forms in such a degree that 

 the characters are fixed by inheritance, so tliat changed external condi- 

 tions cannot influence them again, and farther, there must be kyesame- 

 chania, which prevents hybridization. The possibility, however, of 

 hybridization by artificial means cannot be always regarded as a proof 

 against the value of the respective forms as species : if two species live 

 separated they do not interbreed in nature, and if they are forced to do 

 so, this possibility cannot affect their value as species under normal 

 and natural conditions. 



As separation is reached by degrees, distinct species must have devel- 

 oped gradually, and such must still develop. We know numerous 

 examples of so-called "polymorphous" genera, where apparently the 

 process of formation of species is beginning or not yet accomplished. It 

 is true, variations, varieties, and species pass gradually into each other, 

 but this does not imply that these three terms shall be treated alike, 

 and that there is no difference at all between them. A tree is not a 

 shrub, although there are intermediate growths. So we can give a 

 correct definition of variety and species, although there are intermediate 

 forms, which may be doubted, wliether they belong to the one or the 

 other. 



*This confusion of Weismann's ideas is most evident in the two last pages of his latest 

 publication (" Germinal Selection," The Monist, Vol. 6, No. 2, January, 1896, pp. 292, 29.3). 

 This whole paper is devoted to the demonstration of the action of natural selection as eflfect- 

 ing adaptation, and though he saj-s that " the mode of formation of the living world as a 

 whole " may be understood by this principle ! 



t See I. c, p. 32. 



