Chap. XIII. AND ABORTED ORGANS. 407 



" Ijpo^liuiinjif.s of oro^ans which attain full functional develop- 

 ni(Mit in hiij^hcr verteliratcs." The mammary j^lands of the 

 Oniithorhyncluis may be considered, in comparison Avith the 

 udders of a cow, as in a nascent condition. The oviji^erous 

 frena of certain cirripodes, which are only slightly developed, 

 and which have ceased to give attachment to the ova, are nas- 

 cent branchiir. 



Rudimentary organs are very liable to vary in development 

 and in other respects in the individuals of the same species. 

 Moreover, in closely-allied species, the degree to which the 

 same organ has been reduced occasionally differs much. Tiiis 

 latter fact is well exemplilied in the state of the wings in fe- 

 male moths in certain group.s. Rudimentary organs may be 

 utterly aborted ; and this implies that, in certain animals or 

 plants, parts are entindy absent which analogy would lead us 

 to expect to find, and which are occasionally found in mon- 

 strous individuals. Thus in most of the ijcrophulariaceoe the 

 tifth 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 becomes 

 ])('rfectly developed, as may be seen in the common snap- 

 dragon. In tracing tlie homologies of any part in diflerent 

 members of the same class, nothing is more common, or more 

 necessary, in order fully to understand the relations of the 

 ])arts, than the discovery of rudiments. This is well shown in 

 llic drawings given hy Owen of the bones of the leg of the 

 horse, ox, and rhinocero.s. 



It is an important fact that rudimentary organs, such as 

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

 1)e detected in the embryo, but afterward wholly disappear. It 

 is also, I believe, a universal rule, tliat a rudimentary part is 

 of greater size relatively to the adjoining parts in the embryo, 

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

 rudimentary, or even cannot l)e said to be in any degree rudi- 

 mentary. Hence rudimentary organs in the adult are often 

 said to have retained their embryt)nic condition. 



I have now given the leading facts witli 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 e.\(iuisitely adai)ted for 

 C{>rtain purposes, tells us with e([ual plainness that these rudi- 

 mentary or atrophied organs are imperfect and useless. In 

 works o;i n:iiu!Ml liislnrv, rudimentary organs arc generally 



