RUDIMENTARY ORGANS 407 



reduced organ, modified for a new function : the wing 

 of the Apteryx is useless, and is truly rudimentary. 

 The mammary glands of the Ornithorhynchus may, 

 perhaps, be considered, in comparison with the udder 

 of a cow, as in a nascent state. The ovigerous frena 

 of certain cirripedes, which are only slightly developed 

 and which have ceased to give attachment to the ova, 

 are nascent branchiae. 



Rudimentary organs in the individuals of the same 

 species are very liable to vary in degree of development 

 and in other respects. Moreover, in closely allied 

 species, the degree to which the same organ has been 

 rendered rudimentary occasionally differs much. This 

 latter fact is well exemplified in the state of the wings 

 of the female moths in certain groups. Rudimentary 

 organs may be utterly aborted ; and this implies, that 

 we find in an animal or plant no trace of an organ, 

 which analogy would lead us to expect to find, and 

 which is occasionally found in monstrous individuals 

 of the species. Thus in the snapdragon (antirrhinum) 

 we generally do not find a rudiment of a fifth stamen ; 

 but this may sometimes be seen. In tracing the homo- 

 logies of the same part in different members of a class, 

 nothing is more common, or more necessary, than the 

 use and discovery of rudiments. This is well shown in 

 the drawings given by Owen of the bones of the leg 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 or organ is of greater 

 size relatively to the adjoining parts in the embryo, 

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

 i9 less rudimentary, or even cannot be said to be in any 

 degree rudimentary. Hence, also, a rudimentary organ 

 in the adult is often said to have retained its embryonic 

 condition. 



I have now given the leading facts with respect to 

 rudimentary organs. In reflecting on them, every one 



