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comijletely together with that of one or more other types under certain con- 

 ditions, and the descendants are qualified for propagation ; secondly, the line of 

 descendants remains separate under every condition ; and thirdly, the lines of 

 descendants are partly fused by the appearance of cross-products, which, however, are 

 not fully qualified for propagation. The two first points are the same as those 

 mentioned under monogamic propagation. The third case is of little consequence ; 

 the cross-products, though often obscuring the fact of the independence of the 

 descendants of two given types, have really no influence upon the lines of descend- 

 ants, as the offsjiring of the cross-products soon become extinct, and therefore do not 

 affect the characters of those descendants of the present types which are not cross- 

 products. In asexual and in sexual propagation we observe that the lines of 

 descendants of the various types exhibit this contrast, that they are either capable of 

 fusion or not capable of fusion : in the first case divergent development changes 

 under certain conditions into convergent development, and ends in identity ; in the 

 second case the development ends under every condition in divergency. 



In order to see clearly which kind of divergency in animated nature we shall 

 have to term specific, we will shortly recapitulate those jJoints which have to be taken 

 into consideration. 



1. The presence of morphological distinguishing characters is not a final criterion 

 uf specific distinctness ; a definition of species based solely upon such dift'erences not 

 only would not take into account individual, geographical, and historical polymorphism, 

 but would, if consequently applied, make every individual specifically distinct, as we 

 have seen that the sum of the characters of every individual is different from the 

 sum of the characters of every other individual. 



2. Though according to the theory of evolution every species is the outcome 

 of the transmutation of another, ancestral sjiecies, we have only morphological 

 characters to distinguish ancestral and descendant species by. Therefore, considering 

 what is said under 1, a final criterion whether the difierent types which form tiie 



. direct line of ancestors of a given type are " specifically " different is wanting ; 

 palaeontology provides us with morphologically different specimens, which can never 

 be proved to have been specifically distinct. And as, further, allied species have at 

 a former period not been specifically different, a definition of the term " species " 

 based upon evolution must leave the line of extinct ancestors altogether out of 

 consideration. 



o. As the theorj' of evolution further implies that a species can in the course of 

 time develop into one or more descendant species, the term " species " rigorously 

 applied must be restricted to contemporary individuals. Hence the definition of the 

 term " species " as designating a certain kind, and always the same kind, of diversity 

 throughout animated nature, has to be arrived at by comparing the divergency of 

 coexistent types. 



4. The theory of creation explains the diversity in animated nature by 

 assuming that every species from the time of its special creation to its extinction 

 is a unit separate from every other unit ; allied species have never been and will 

 never be the same. The theory of evolution, abandoning special creation of each 

 species, puts in its place divergent development from a common form, but to explain 

 the actually existing great discrepancy in nature must assume, like the theory of 

 creation, that when a certain degree of divergency is attained the form of animal or 

 plant exhibiting this divergency can never become one with any other form. This 

 degree of divergency stands in the same contraposition to all lower degrees of 



