The term abortive organ has been thus applied to above structure (as _invariable_ as all other parts{167}) from their absolute similarity to monstrous cases, where from _accident_, certain organs are not developed; as infant without arms or fingers with mere stump representing them: teeth represented by mere points of ossification: headless children with mere button,--viscera represented by small amorphous masses, &c.,--the tail by mere stump,--a solid horn by minute hanging one{168}. There is a tendency in all these cases, when life is preserved, for such structures to become hereditary. We see it in tailless dogs and cats. In plants we see this strikingly,--in Thyme, in _Linum flavum_,--stamen in _Geranium pyrenaicum_{169}. Nectaries abort into petals in Columbine <_Aquilegia_>, produced from some accident and then become hereditary, in some cases only when propagated by buds, in other cases by seed. These cases have been produced suddenly by accident in early growth, but it is part of law of growth that when any organ is not used it tends to diminish (duck's wing{170}?) muscles of dog's ears, <and of> rabbits, muscles wither, arteries grow up. When eye born defective, optic nerve (Tuco Tuco) is atrophied. As every part whether useful or not (diseases, double flowers) tends to be transmitted to offspring, the origin of abortive organs whether produced at the birth or slowly acquired is easily understood in domestic races of organisms: [a struggle between the atrophy and hereditariness. Abortive organs in domestic races.] There will always be a struggle between atrophy of an organ rendered useless, and hereditariness{171}. Because we can understand the origin of abortive organs in certain cases, it would be wrong to conclude absolutely that all must have had same origin, but the strongest analogy is in favour of it. And we can by our theory, for during infinite changes some organ, we might have anticipated, would have become useless. <We can> readily explain the fact, so astounding on any other view, namely that organs possibly useless have been formed often with the same exquisite care as when of vital importance. {167} I imagine the meaning to be that abortive organs are specific characters in contrast to monstrosities. {168} Minute hanging horns are mentioned in the _Origin_, Ed. i. p. 454, vi. p. 625, as occurring in hornless breeds of cattle. {169} _Linum flavum_ is dimorphic: thyme gynodiaecious. It is not clear what point is referred to under _Geranium pyrenaicum_. {170} The author's work on duck's wings &c. is in _Var. under Dom._, Ed. 2, i. p. 299. {171} The words _vis medicatrix_ are inserted after "useless," apparently as a memorandum.