( 428 ) 



In order to avoid similar confusion we have to come to a conclusion which 

 definition of the term " species " as opposed to the lower degrees of variation we will 

 accept, before we discuss the variability of the genital armature within the limits of 

 a " species." 



As most of us pretend to be evolutionists, let us take it as an axiom, which we 

 need not discuss here any more, that the great divergency exhibited in animated 

 nature is the result of the development of the various forms of animals and 

 plants from a common ancestor. Before Darwin brought forward his theory of 

 evolution naturalists had to solve one question : which are the differences found to 

 exist among the various forms of animals and jjlants ? The question which is put to 

 naturalists nowadays is, however, twofold : (1) which kinds of divergency do we find 

 to exist in nature ? (2) how has this divergency come about ? 



It seems to us to be a rather general assumption amongst naturalists, no matter 

 whether they treat animated nature fi-om the point of view of a philosopher, or 

 whether they work with the individual specimens, that the variation of the individuals 

 which belong to a complex called species is such that, with the exception of marked 

 di- and polymorphism, we can draw up a series of specimens which form a con- 

 tinuous chain from one extreme variety to the other, the differences between the 

 adjoining links being extremely slight. And it is almost natural that the assumption 

 should be so general. The question which governs zoological work is one of specific 

 differences on the side of us systematists, and one of the causes of the specific and 

 non-specific characters on the side of the biologists, and over the. consideration of 

 " characters " it has been lost sight of that speaking of a specific character and the 

 variabiUty of characters means, in fact, speaking of abstracta, while our work must 

 be based upon concreta, upon the individual specimens. The variation of an organ 

 may be continuous ; in a series of individuals a certain organ may even be con.staut ; 

 but that does by no means imply that the individuals as opposed to one of their 

 organs form a continuous chain. An individual has many " characters," and these 

 do not var}' in the same manner and degree in the various specimens ; some indi- 

 viduals may be almost identical in one or some characters, while they are widely 

 different in other respects, and this will at once become manifest to everybody who 

 actually tries to put together a " continuous " series of specimens. An illustration will 

 bring the fact more closely to mind. A, B, C, D may represent individuals ; a, b, c, 

 three characters ; a}, a', ii?, a', etc., V, b\ etc., c', C", (?, etc., may be minute degrees 

 of development of the characters. Now, if we arrange the individuals according 

 to the gfradual development of the character a, and thus have a continuous series in 

 respect to this character, the chain of individuals will nevertheless be discontinuous, 

 as in the following diagram : — 



A B C D . . . . 



«' «- a' a' . . . . 



6'° i' i« 6" .... * 



c' c' c' c" . . . . 



If we further arrange the series according to the continuity of character b or c, 

 not only will the individuals A, B, C . . . stand in other places within the new 

 series, but also new individuals must be introduced to make the chain again con- 

 tinuous. Hence it will be sufficiently clear that, notwithstanding the variation of every 

 organ of a species may be continuous, the individuals each being a sum of organs 



