GOOD AND BAD SPECIES. 273 
themselves, and at length cease to be any longer connected 
with the original primary species through intermediate forms 
of transition. Thus arise “good species” out of varieties. 
Thus, then, the struggle for life necessarily favours the 
general divergence of organic forms, that is, the constant 
tendency of organisms to form new species. This fact does 
not rest upon any mystic quality, or upon an unknown forma- 
tive tendency, but upon the interaction of Inheritance and 
Adaptation in the struggle for life. As the intermediate 
forms, that is, the individuals in a state of transition, of 
the varieties of every species die out and become extinct, 
the process of divergence constantly goes further, and from 
the extremes forms develop which we distinguish as new 
species. 
Although all naturalists have been obliged to acknowledge 
the variability and mutability of all species of animals and 
plants, yet most of them have hitherto denied that the 
modification or transformation of the organic form surpasses 
the original limit of the characters of the species. Our 
opponents cling to the proposition—“ However far a species 
may exhibit deviations from its usual form in a collection of 
varieties, yet the varieties of it are never so distinct from 
one another as two really good species.” This assertion, 
which Darwin’s opponents usually place at the head of 
their arguments, is utterly untenable and unfounded. 
This will become quite clear as soon as we critically 
compare the various attempts to define the idea of species. 
No naturalist can answer the question as to what is in 
reality a “genuine or good species” (“bona species ”) ; yet 
every systematic naturalist uses this expression every day, 
and whole libraries have been written on the question as to 
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