102 DISCRIMINATIONS CHAP. 



converse is true, namely, what may be 

 called the fluidity, or perpetual instability, 

 of species. There is at least one possible, 

 and even probable, alternative between 

 these two extreme alternatives. It is 

 surely a curious fact that the two 

 greatest naturalists of the modern world, 

 Cuvier and Linnaeus, whose minds were 

 brought by their special pursuits into the 

 closest possible contact with the only 

 facts in Nature that have a direct bear- 

 ing on this question, were both of them 

 not only convinced of the stability of 

 species, but recognised it as the essential 

 foundation of all their work. Stability, 

 however, was the word they used, not 

 immutability. Classification was their 

 special work, and the whole principle of 

 classification, as Mr. Spencer truly says, 

 rests on the idea, and on the fact, that 

 all living creatures can be arranged in 

 groups by endless cycles of definite 



