2o THE SCIENTIFIC EVIDENCES OF 



were tracing the lines of genetic relationship. 

 For, be it observed, a scientific or natural classi- 

 fication differs very much from a popular or 

 hap-hazard classification, and the difference consists 

 in this, that while a popular classification is framed 

 with exclusive reference to the external appear- 

 ance of organisms, a scientific classification is 

 made with reference to the whole structure. A 

 whale, for instance, is often thought to be a fish, 

 because it resembles a fish in form and habits ; 

 whereas dissection shows that it is beyond all 

 comparison more unlike a fish than it is like a 

 horse or a man. This is, of course, an extreme 

 case ; but it was cases such as this that first led 

 naturalists to see that there are resemblances 

 between organisms much more deep and im- 

 portant than appear upon the surface ; and con- 

 sequently, that if a natural classification was 

 possible at all, it must be made with reference 

 to these deeper resemblances. Of course, it took 



