68 EVOLUTION OF TO-DAY. 



The Value of this Tree-like Classification. 

 When now this sort of classification, as taught by 

 anatomy, paleontology, and embryology, with its 

 implied theory of genetic descent, comes to be ap- 

 plied to interpreting the existing animal kingdom, 

 it is found that a wonderful light is thrown upon 

 the whole subject. This conception has, of course, 

 gradually grown out of the older one, and has only 

 step by step taken its place. The nominal relation- 

 ship of animals remains, therefore, much the same 

 as it has always been, although many are now 

 classed together which were previously thought to 

 be separate, and many are now widely separated 

 which were previously thought to be closely re- 

 lated, and many animals whose relationship was 

 formerly a complete mystery, are now easily under- 

 stood. For the term relation has now a meaning, 

 and it is seen that an animal may be a vertebrate, 

 and still show some relationship to other types. To 

 use the words of a modern writer : " All the enigmas 

 of structure become resolved ; representative and 

 aberrant, progressive and degraded, synthetic and 

 isolated, persistent and prophetic types no longer 

 baffle comprehension." It becomes evident that 

 there is a real meaning to the term natural classifica- 

 tion, a fact long since recognized, but not understood. 

 We can understand now why it is that organs of 

 the least importance to the animal are usually of the 

 greatest weight in classification ; for organs of no 

 functional importance can only be explained by in- 

 heritance from some ancestor in which they were 

 useful ; and since they are of no present value, they 



