CHAPTER III. 



VESTIGIAL PARTS. 



UNDER the term vestigial it will be convenient to 

 consider those parts commonly described as rudimentary, 

 abortive, atrophied, or useless. On the whole it is 

 better to refer to these structures as vestigial. In 

 dealing with such examples as the denticles of the 

 narwhal, which never cut the gum, the teeth of orni- 

 thorhynchus, or the splint-bones of horses, we have un- 

 mistakable evidence that they are remnants of structures 

 which were functional in the ancestors of these animals. 

 In many instances it is not easy to decide whether 

 a diminutive, or feebly grown part, in one animal is the 

 remnant of an organ better grown in its ancestors, or 

 the rudiment of an organ which has arrived at a higher 

 degree of perfection in its descendants. 



This is illustrated in the hind limbs of whales. If 

 we regard cetaceans as living representatives of land 

 mammals which have taken to water, the hind limbs 

 are remnants ; on the other hand, if the descendants 

 of cetaceans have acquired terrestrial habits, then, the 

 hind limbs which do not project beyond the skin, but 

 are deeply buried in the blubber, must be considered 

 rudimentary or incipient structures. The whale is 

 merely selected as an illustration of the advantage or 



