RUDIMENTARY ORGANS 493 



tirely absent which analogy would lead us to expect to find in 

 them, and which are occasionally found in monstrous indi- 

 viduals. Thus in most of the Scrophulariaceae the fifth 

 stamen is utterly aborted; yet we may conclude that a fifth 

 stamen once existed, for a rudiment of it is found in many 

 species of the family, and this rudiment occasionally be- 

 comes perfectly developed, as may sometimes be seen in the 

 common snap-dragon. In tracing the homologies of any 

 part in different members of the same class, nothing is more 

 common, or, in order fully to understand the relations of the 

 parts, more useful than the discovery of rudiments. This is 

 well shown in the drawings given by Owen of the leg-bones 

 of the horse, ox, and rhinoceros. 



It is an important fact that rudimentary organs, such as 

 teeth in the upper jaws of whales and ruminants, can often 

 be detected in the embryo, but afterwards wholly disappear. 

 It is also, I believe, a universal rule, that a rudimentary part 

 is of greater size in the embryo relatively to the adjoining 

 parts, than in the adult; so that the organ at this early age is 

 less rudimentary, or even cannot be said to be in any degree 

 rudimentary. Hence rudimentary organs in the adult are 

 often said to have retained their embryonic condition. 



I have now given the leading facts with respect to rudi- 

 mentary organs. In reflecting on them, every one must be 

 struck with astonishment ; for the same reasoning power 

 which tells us that most parts and organs are exquisitely 

 adapted for certain purposes, tells us with equal plainness 

 that these rudimentary or atrophied organs are imperfect and 

 useless. In works on natural history, rudimentary organs 

 are generally said to have been created "for the sake of 

 symmetry," or in order "to complete the scheme of nature." 

 But this is not an explanation, merely a re-statement of the 

 fact. Nor is it consistent with itself: thus the boa-constrictor 

 has rudiments of hind-limbs and of a pelvis, and if it be 

 said that these bones have been retained "to complete the 

 scheme of nature," why, as Professor Weismann asks, have 

 they not been retained by other snakes, which do not possess 

 even a vestige of these same bones ? What would be thought 

 of an astronomer who maintained that the satellites revolve 

 in elliptic courses round their .planets 'for the sake of sym- 



