Weismann suggests that the morbid condition of the nervous system may be due to some infection such as might arise from microbes, which find a home in the mutilated and disordered nervous system in the parent, and subsequently transmit themselves to the offspring through the reproductive elements, as the infections of various diseases appear to do--the muscardine silkworm disease in particular being known to be conveyed to offspring in this manner. But whether we can discover the true explanation or not, inherited mutilations can hardly be accounted for as the result of a general tendency to inherit acquired modifications. How could a factor which seems to be totally inoperative in cases of ordinary mutilation, and only infinitesimally operative in transmitting the normal effects of use and disuse, suddenly become so powerful as to completely overthrow atavism, and its own tendency to transmit the non-mutilated type of one of the parents and of the non-mutilated type presented by the injured parent in earlier life? Does not so striking and abrupt an intensification of its usually insignificant power demand an explanation widely different from that which might account for the extremely slow and slight inheritance of the normal effects of use and disuse? Surely it would be better to suspend one's judgment as to the true explanation of highly exceptional and purely pathological cases rather than resort to an hypothesis that creates more difficulties than it solves. THE MOTMOT'S TAIL. The narrowing of the long central tail feathers of the motmot is attributed to the inherited effects of habitual mutilation (_Descent of Man_, pp. 384, 603). But in the specimens at South Kensington[61] the narrowness extends upwards much beyond the habitually denuded part, and the broadened end is the broadest part of the whole feather. If the inherited effect of an inch or two of denudation extends from three to six inches upwards, why has it not also extended two inches downwards so as to narrow the broadened end? The narrowness seems to be a mainly relative or negative effect produced by the broadening out of a long tapering feather at its end under the influence of sexual selection. Several other birds have similarly narrowed or spoon-shaped feathers and do not bite them. Is it not more feasible to suppose that this attractive peculiarity first suggested its artificial intensification, than to suppose that the bird began nibbling without any definite cause? Sexual selection would then encourage the habit. Anyhow, it is as impossible to show that the mutilation preceded the narrowing as it is to show that tonsure preceded baldness. OTHER INHERITED INJURIES MENTIONED BY DARWIN.