242 Darwin, and after Darwin. 



before either Galton or Weismann had questioned 

 the transmission of acquired characters. However. 

 I allow that this line of argument has now become 

 for the time being at all events a dubious line, and 

 will therefore at once pass on to the second line, 

 which is not open to doubt from any quarter. 



Whether or not we accept Weismann's views, it 

 will here be convenient to employ his terminology, 

 since this will serve to convey the somewhat im- 

 portant distinctions which it is now my object to 

 express. 



In the foregoing paragraphs, under heading (A), we 

 have seen that there must be "literally numberless 

 forms" which have been ranked as true species, 

 whose diagnostic characters are nevertheless not 

 congenital. In the case of plants especially, we know 

 that there must be large numbers of named species 

 which do not conform to the criterion of Heredity, 

 although we do not know which species they are. 

 For present purposes, however, it is enough for us 

 to know that there are many such named species, 

 where some change of environment has acted directly 

 and similarly on all the individual " somas " exposed 

 to it, without affecting their "germ-plasms," or the 

 material bases of their hereditary qualities. For named 

 species of this kind we may employ the term somato- 

 genetic species. 



But now, if there are any cases where a change of 

 environment does act on the germ-plasms exposed to 

 it, the result would be what we may call blasto- 

 genetic species i.e. species which conform to the 

 criterion of Heredity, and would therefore be ranked 

 by all naturalists as "true species." It would not 



