8o Permanence and Evolution. 



possible, however unlikely, that some day we 

 may find a true horse contemporary with 

 orohippus ; and although every intermediate 

 link may have been in particular instances 

 attempted to be traced, the general aspect of 

 palaeontology is, as we know it, not favourable 

 to the origin of marked types by slow grada- 

 tions. Nothing requires more care than the 

 tracing of supposed intermediate links between 

 types of large generality. In one sense every 

 organic type is intermediate between two or more 

 others, and yet how difficult do naturalists find it 

 to classify say the Ruminantia or Carnivora in a 

 regular series, how much more fossil animals, of 

 whom we have only a limited number of usually 

 imperfect remains of the bony parts only. 



In a number of instances we are able to show 

 that differences so slight as to appear likely to 

 be most variable are in reality most permanent ; 

 let us take external colour (commonly called 

 fleeting and variable) as an instance. And here 



