Castration, it is true, profoundly affects these characters. In the case of Deer it inhibits the growth of antlers, in Cattle the horns are increased in length but reduced in thickness—they are longer than those of the female, but resemble them in appearance, and further, the whole stature is greatly increased, but it is at the same time conspicuously less massive, particularly at the neck and fore-quarters. In eunuchs it results in immense stature and the loss of the more characteristic male features, such as the beard and the bass voice. The removal of the testes in birds is always a difficult operation and is rarely successfully performed. Hence the accounts of changes in plumage consequent on this operation are inconclusive. It has generally been supposed that whenever, either by removal or by disease, the testes are rendered inoperative the plumage, when normally of a resplendent type, assumes the coloration of the female. This is probably an erroneous supposition, but what happens is a failure to secrete the more intense pigments and the more specialized forms of feathers, so that the resultant dress answers to the juvenile male dress. It is not a case of “reversion” to this livery, but a failure to assume the latest acquirements of the species. These, as has already been shown, are only very gradually developed. The intensity of pigmentation, or concentration of pigmentation, which results in sharply defined areas of colour, is a cumulative process. As it loses in intensity at any given moult, so the individual tends to reproduce the phases of the earlier and vanishing livery. Sooner or later, however, this earlier livery disappears more or less completely: is eliminated from the system, so to speak: and what is commonly called lack of “vigour” results, not in a return to the earlier, sombre dress, but in the later-acquired, resplendent plumage lacking intensity. The seasonal, temporary secondary sexual character has become, as some say, a “somatic” character. Highly probable as this view appears, it ought, it may be argued, to receive support from nestling plumages. Young gulls, for example, should occasionally revert from the mottled to the earlier striped livery. But we have no evidence of this; and it does not follow that this sequence of events should occur. The conditions of control are different.