Would it not be better on the whole if each individual took a fresh start as far as possible on the advantageous typical lines laid down by natural selection? Through the long stages of evolution from primaeval protoplasm upwards, such species as were least affected by use-inheritance would be most free to develop necessary but seldom-used organs, protective coverings such as shells or skulls, and natural weapons, defences, ornaments, special adaptations, and so forth; and this would be an advantage--for survival would obviously depend on the _importance_ of a structure or faculty in deciding the struggle for existence and reproduction, and not on the total amount of its using or nourishment. If natural selection had on the whole favoured this officious ally and frequent enemy, surely we should find better evidence of its existence. Without laying undue stress upon the evil effects of use-inheritance, a careful examination of them in detail may at least serve to counter-balance the optimistic _a priori_ arguments for belief in that plausible but unproven factor of evolution. The benefits derivable from use-inheritance are largely illusory. The effects of _use_, indeed, are generally beneficial up to a certain point; for natural selection has sanctioned or evolved organs which possess the property or potentiality of developing to the right extent under the stimulus of use or nourishment. But use-_inheritance_ would cumulatively alter this individual adaptability, and would tend to fix the size of organs by the average amount of ancestral use or disuse rather than by the actual requirements of the individual. Of course under changed conditions involving increased or lessened use of parts it might become advantageous; but even here it may prove a decided hindrance to adaptive evolution in some respects as well as an unnecessary aid in others. Thus in the case of animals becoming heavier, or walking more, it would _lengthen_ the legs although natural selection might require them to be shortened. In the Aylesbury duck and the Call duck, if use-inheritance has increased the dimensions of the bones and tendons of the leg, natural selection has had to counteract this increase so far as length is concerned, and to effect 8 per cent. of shortening besides. If use-inheritance thickens bones without proportionally lengthening them, it would hinder rather than help the evolution of such structures as the long light wings of birds, or the long legs and neck of the giraffe or crane. VARIED EFFECTS OF USE AND DISUSE.