378 Thoughts on Species. 



There is then a fixed normal condition or value, and around 

 it librations take place. There is a central or intrinsic law which 

 prevents a species from being drawn off to its destruction by any 

 external agency, while subject to greater or less variations under 

 extrinsic forces. 



Liability to variation is hence part of the law of a species ; 

 and we cannot be said to comprehend in any case the complete 

 idea of the type until the relations to external forces are also 

 known. The law of variables is as much an expression of the 

 fundamental equalities of the species in organic as in inorganic 

 nature ; and it should be the great aim of science to investigate 

 it for every species. It is a source of knowledge which will yet 

 give us a deep insight into the fundamental laws of life. Varia- 

 tions are not to be arranged under the head of accidents : for 

 there is nothing accidental in nature ; what we so call, are ex- 

 pressions really of profound law, and often betray truth and law 

 which we should otherwise never suspect. 



This process of variation, is the external revealing the inter- 

 nal, through their sympathetic relations ; it is the law of univer- 

 sal nature reacting on the law of a special nature, and compell- 

 ing the latter to exhibit its qualities ; it is a centre of force mani- 

 festing its potentiality, not in its own inner working, but in its 

 outgoings among the equibrating forces around, and thus offer- 

 ing us, through the known and physical, some measure of the 

 vital within the germ. It is therefore one of the richest sources 

 of truth open to our search. 



The limits of variation, it may be difficult to define among 

 species that have close relations. But being sure that there are 

 limits — that science, in looking for law and order written out in 

 legible characters, is not in fruitless search, we need not despair 

 of discovering them. The zoologist, gathering shells or mollusks 

 from the coast of eastern America and that of Japan, after care- 

 ful study, makes out his lists of idential species, with the full 

 assurance that species are definite and stable existences ; and he 

 is even surprised with the identity of characters between the 

 individuals of a species gathered from so remote localities. And 

 as he sees zoological geography rising into one of the grandest 

 of the sciences, his faith in species becomes identified with his 

 faith in nature and all physical truth. j. 



If then we may trust this argument from general truths to 

 special, — general truths I say, for general principles as far as 



