ARE SPECIES STABLE? 33 



ranked by one as true species are ranked by another 

 as simple varieties. If two animals are quite like 

 each other they will usually be called varieties ; if 

 quite unlike they will be called species. But no one 

 has been able to tell us how a line can be drawn by 

 which we can decide whether two forms are unlike 

 enough to be called species. This confusion makes 

 it utterly impossible to come to any conclusion as to 

 the mutability of species. Species are . generally 

 considered to be so distinct as not to be connected 

 by intermediate forms, while varieties are thus con- 

 nected. If, therefore, the evolutionist shows that 

 any two well-defined species are thus connected, 

 they immediately lose their rank as species and be- 

 come simple varieties. Thus the whole force of the 

 proof is lost. When, as above described, the Rus- 

 sian naturalist showed that Artemia could be con- 

 verted into Branchippus, it would seem that 

 something had been proved. These forms had 

 always been considered distinct species, and doubt- 

 less would have been so regarded were it not for 

 this demonstrated connection between them. But 

 now it is evident that they can be regarded as the 

 fresh- and salt-water varieties of the same species. 

 Indeed, they must be so regarded or the immuta- 

 bility of species is proved. Thus the argument is 

 inevitably in a circle. The naturalist, by long study, 

 succeeds in uniting, by intervening varieties, two 

 forms which are considered as distinct species, only 

 to have the satisfaction of seeing that he has shown 

 them to be varieties of one species. And thus, un- 

 til a very large number of species have been united, 

 this phantom chase will continue. 



