96 THE DARWINIAN THEORY 



because moles are descended from mammals in 

 which the eyes were functionally active. Through 

 the burrowing habits of the mole, the eyes have 

 become degenerate and rudimentary ; but owing to 

 the law of Recapitulation, they are still developed. So 

 with whalebone whales, which are toothless when 

 adult, the presence of teeth at an early stage of 

 development can only be explained by the descent 

 of whalebone whales from toothed ancestors. 



Rudimentary organs are of exceedingly common 

 occurrence ; indeed there are probably few if any of 

 the higher animals in which some may not be found. 

 Thus the splint-bones of a horse's leg are rudiments 

 of the metacarpals or metatarsals of the second and 

 fourth digits of the manus or pes, which were fully 

 developed in the extinct Hipparion, and in other 

 more remote ancestors of the horse. Almost all 

 parasitic animals undergo, as we have seen, retro- 

 gressive or degenerative change in certain parts 

 or the whole of their structure, and it commonly 

 happens that vestiges of these lost organs linger on 

 as rudiments, whose presence would be inexplicable 

 but for the history of their formation. 



Man himself is no exception to the rule. The 

 muscles of the ear, whereby it can be pulled upwards 

 or twitched forwards or backwards, are in a degener- 

 ate condition, and comparatively few men have any 

 real power over them ; while other smaller muscles 

 which run from one part of the ear to another, are 

 in such a completely rudimentary state, that but for 

 anatomy their presence would never be suspected. 



There are other parts of man's bodily structure—: 



