No. 580] ORIGIN OF SINGLE CHARACTERS 



197 



is a character, the color of the horse's hair is a character, 

 the most minute cellular structure of the tissue of the 

 hoof is a character. 



There is an underlying reason why this very elastic 

 use of the term is absolutely scientific: it is, that every 

 one of the above diverse applications of the term to animal 

 or plant life refers to some structure or sonic quality 

 which is heritable; heredity is the unifying principle. 



The word is again elastic and often confusing in being 

 used both for germinal characters which are always herit- 

 able and for bodily modifications of character acquired 

 through habit or environment which may not be heritable. 

 When we speak of characters which are not known to be 

 hereditary we should qualify them as acquired, as modi- 

 fied, as due to nurture, to habit or ontogeny, to environ- 

 ment, as somatic rather than as germinal. Thus it is per- 

 fectly proper to speak of " ontogenetic species" as Jordan 

 does, species the bodily characters of which are due to 

 certain habits; or of "environmental species" the bodily 

 characters of which are due to peculiarities of environ- 

 ment. While such modifications by habit and by en- 

 vironment make up a considerable part of the characters 

 which distinguish geographic species, subspecies and 

 races, it is not the origin and the transformation of these 

 characters which we are now considering, for that prob- 

 lem is comparatively simple, but rather of those under- 

 lying germinal and heritable characters the origin and 

 transformation of which is absolutely an impenetrable 

 mystery at the present time. 



How do we know through zoology, botany, and paleon- 

 tology as well as through experiment that "characters" 

 are real units of structure with some individual and dis- 

 tinct qualities and properties of their own which separate 

 them from all their fellows and at the same time with 

 certain properties of correlation which unite them with 

 all their fellows! 



First, we may observe in these living and extinct forms 

 evidences of two such antithetic principles, a principle 



