I think these facts are sufficient to render it probable that at whatever period of life any peculiarity (capable of being inherited) appears, whether caused by the action of external influences during mature life, or from an affection of the primary germinal vesicle, it _tends_ to reappear in the offspring at the corresponding period of life{474}. Hence (I may add) whatever effect training, that is the full employment or action of every newly selected slight variation, has in fully developing and increasing such variation, would only show itself in mature age, corresponding to the period of training; in the second chapter I showed that there was in this respect a marked difference in natural and artificial selection, man not regularly exercising or adapting his varieties to new ends, whereas selection by nature presupposes such exercise and adaptation in each selected and changed part. The foregoing facts show and presuppose that slight variations occur at various periods of life _after birth_; the facts of monstrosity, on the other hand, show that many changes take place before birth, for instance, all such cases as extra fingers, hare-lip and all sudden and great alterations in structure; and these when inherited reappear during the embryonic period in the offspring. I will only add that at a period even anterior to embryonic life, namely, during the _egg_ state, varieties appear in size and colour (as with the Hertfordshire duck with blackish eggs{475}) which reappear in the egg; in plants also the capsule and membranes of the seed are very variable and inheritable. {474} _Origin_, Ed. i. p. 444, vi. p. 610. {475} In _Var. under Dom._, Ed. ii. vol. I. p. 295, such eggs are said to be laid early in each season by the black Labrador duck. In the next sentence in the text the author does not distinguish the characters of the vegetable capsule from those of the ovum.