Chap. xiv. and A borted Organs. 399 



useless, and is truly rudimentary. Owen considers the simple fila- 

 mentary limbs of the Lepidosiren as the " beginnings of organs 

 which attain full functional development in higher vertebrates ; " 

 but, according to the view lately advocated by Dr. Giinther, they 

 are probably remnants, consisting of the persistent axis of a fin, 

 with the lateral rays or branches aborted. The mammary glands of 

 the Ornithorhynchus may be considered, in comparison with the 

 udders of a cow% as in a nascent condition. The ovigerous frena of 

 certain cirripedes, which have ceased to give attachment to the 

 ova and are feebly developed, are nascent branchias. 



Rudimentary organs in the individuals of the same species are 

 very liable to vary in the degree of their development and in other 

 respects. In closely allied species, also, the extent to which the 

 same organ has been reduced occasionally differs much. This latter 

 fact is well exemplified in the state of the wings of female moths 

 belonging to the same family. Rudimentary organs may be utterly 

 aborted ; and this implies, that in certain animals or plants, parts 

 are entirely absent which analogy w 7 ould lead us to expect to find in 

 them, and which are occasionally found in monstrous individuals. 

 Thus in most of the Scrophulariacese 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 becomes perfectly developed, as may some- 

 times be seen in the common snap-dragon. In tracing the homo- 

 logies 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 rudimen- 

 tary organs in the adult are often said to have retained their 

 embryonic condition. 



I have now given the leading facts with respect to rudimentary 

 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 



