ITS PLACE IX NATUBE 



5 



in the horse, are so reduced in size or altered in cha- 

 racter as to be of little or not any use in its economy. 



Parts, usually called rudimentary, may be in one of 

 two conditions: either nascent, or in process of growth 

 to something larger and more useful ; or vestigial — that 

 is, in a dwindling and degenerate state, vestiges of a 

 once more developed condition. In any particular 

 case, it may be difficult to say to which category it 

 should be assigned, and we may have to look for guid- 

 ance beyond the mere structure itself. In all or nearly 

 all which we shall meet with in the horse, the presence 

 of the same parts in a fully developed state in other 

 allied though less specialised animals points clearly to 

 the second condition, a conclusion which is strengthened 

 by the certain knowledge derived from palaeontology 

 that the horse in its present form has only come into 

 existence at a very late period of the world's history 

 — is, in fact, one of the most modern forms of animal / 

 known. 



In tracing the history and affinities of animals, 

 rudimentary organs are looked upon by naturalists as 

 far more important than highly developed or functional 

 parts. As Darwin says, they c may be compared with 

 the letters of a word, still retained in the spelling but 

 become useless in the pronunciation, but which serve 

 as a clue for its derivation. 1 On the view of descent 

 1 As, for example, the b in 4 debt ' and 1 doubt.' 



