492 ORIGIN OF SPECIES 



are either quite useless, such as teeth which never cut through 

 the gums, or almost useless, such as the wings of an ostrich, 

 which serve merely as sails. As organs in this condition 

 would formerly, when still less developed, have been of even 

 less use, than at present, they cannot formerly have been 

 produced through variation and natural selection, which acts 

 solely by the preservation of useful modifications. They 

 have been partially retained by the power of inheritance, and 

 relate to a former state of things. It is, however, often 

 difficult to distinguish between rudimentary and nascent 

 organs; for we can judge only by analogy whether a part is 

 capable of further development, in which case alone it de- 

 serves to be called nascent. Organs in this condition will 

 always be somewhat rare; for beings thus provided will 

 commonly have been supplanted by their successors with the 

 same organ in a more perfect state, and consequently will 

 have become long ago extinct. The wing of the penguin 

 is of high service, acting as a fin; it may, therefore, repre- 

 sent the nascent state of the wing: not that I believe this to 

 be the case; it is more probably a reduced organ, modified 

 for a new function: the wing of the Apteryx, on the other 

 hand, is quite useless, and is truly rudimentary. Owen con- 

 siders the simple filamentary limbs of the Lepidosiren as the 

 "beginnings of organs which attain full functional develop- 

 ment in higher vertebrates ;" but, according to the view lately 

 advocated by Dr. Giinther, they are probably remnants, con- 

 sisting of the persistent axis of a fin, with the lateral rays or 

 branches aborted. The mammary glands of the Ornitho- 

 rhynchus 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 branchiae. 



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 en- 



