ITS PLACE IN NATUKE. 5 



structures which correspond to some which are fully 

 developed and functional in other animals, but which, 

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

 character 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 ves- 

 tigial — 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 guidance 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 de- 

 veloped state in other allied though less specialized 

 animals points clearly to the second condition, a con- 

 clusion which is strengthened by the certain knowl- 

 edge 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 "may be 

 compared with the letters of a word, still retained in 



