E VI DEN CBS OF E VOL UTION. 97 



damental thing first on the ground of fact, and 

 then from the philosophy of the case. Practically, 

 no botanist can say what amount of dissimilarity is 

 compatible with the unity of species ; in wild plants 

 it is sometimes very great, in cultivated races often 

 enormous." 1 What the learned professor here af- 

 firms of plants, may likewise, with equal truth, be 

 predicated of animals both wild and domestic. 



Difficulties Regarding Species. 



What, then, is species? Is it something real, as 

 some have averred, or is it, as others maintain, some- 

 thing which is only ideal? And if it have an exist- 

 ence, real or ideal, how may it be recognized? The 

 definitions given do not, as we have seen, throw 

 much light on the subject. On the contrary, they 

 are all more or less defective, and often quite con- 

 tradictory. 



It is only, however, when we come to consider 

 the practical applications of these or similar defini- 

 tions, that we find how illusory and unsatisfactory 

 they are. We have but to compare the classifica- 

 tions of different botanists and zoologists when 

 treating of the same florae and faunae, to realize how 

 utterly inadequate are even the best definitions of 

 species as guides in the classificatory work of prac- 

 tical naturalists. No two naturalists, it may safely 

 be asserted, have ever yet agreed on the same clas- 

 sification as to species, even for the animals and 

 plants of restricted geographical areas. Some aug- 



lu Darwiniana," p. 203. 

 E.-? 



