46 EVOLUTION 



A practical study of the species of plants and 

 animals, and of the way one category of 

 classification includes those beneath it — 

 classes, orders; orders, families; families, 

 genera; genera, species; species, varieties; 

 and varieties, individuals — gives us "an 

 impression of affiliation" which we do not 

 get from a classification of rocks or other 

 inanimate objects. It is impossible not to 

 feel in biological classification the suggestion 

 of pedigrees and heraldry. 



Vestigial Structures. — Both in plants 

 and animals it is common to find minute and 

 more or less useless representatives of organs 

 which are well developed and functional in 

 related forms. It is impossible for us now- 

 adays to keep from calling these structures 

 vestigial (a better term than rudimentary, 

 which should be kept for what is incipient), 

 and from regarding them as the tell-tale 

 evidences of remote ancestry. Darwin com- 

 pared them to the unsounded letters in many 

 words, such as the "o" in leopard, the "b" 

 in doubt, the "g" in reign, which are quite 

 functionless, but tell us something about the 

 history of these words. Every one is famil- 

 iar with the numerous functionless flaps and 

 buttons in clothing w^hich once had a mean- 

 ing they have now lost. Similar "vesti- 

 gial structures" or "survivals" persist in 



