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Show 130 DARWINISM CIIAJ>, this time soft and flexible, tho constant repetition of this effort causes the eye gradually to move round the head till it comes to tho upper side. Now if we suppose this process, which in the young is completed in a few days or weeks, to have boon spread over thousands of generations during the development of these fish, those usually surviving whoso eyes retained more and more of tho position into which the young fish tried to twist them, tho chango becomes intelligible ; though it still remains one of the most extraordinary cases of degeneration, hy which symmetry-which is so universal a characteristic of the higher animals-is lost, in order that the creature may be adapted to a new mode of life, whereby it is enabled the better to escape danger aud continue its existence. The most difficult case of all, that of the eye-the thought of which even to the last, Mr. Darwin says, "gave him a cold shiver" -is nevertheless shown to be not unintelligible; granting of course the sensitiveness to light of some forms of nervous tissue. For he shows that thoro are, in several of tho lower animals, rudiments of eyes, consisting merely of pigment cells covered with a translucent skin, which may possibly serve to distinguish light from darkness, but nothing more. Then we have an optic nerve and pigment cells; then we find a hollow filled with gelatinous substance of a convex form-the first rudiment of a lens. Many of tho succeeding steps are lost, as would necessarily be the case, owing to the great advantage of each modification which o-avo increased disti?~tness o~ vision, the creatures possessin; it inevit~tbly survivmg, while those below them became extinct. But we can. w~ll unde~stand how, after the first step was taken, every v.anatwn tendmg to more complete vision would be preserved till we reached the perfect eye of birds and mammals. Even thi~, as we know, is 1!ot absolutely, but only relatively, perfect. N 01ther the ch~omatic nor the spherical aberration is absolutely c~rrected ; W~Ile long- and short- sightednoss, and the various diseases and Imperfections to which the eye is liable, may be looked upon as relics of the imperfect condition from which the eye has been raised by variation and natural selection. These few examples of difficulties as to the orio-in of remarkable or complex organs must suffice hero· but tho reader who wishes further information on the matte; may study carefully VI DIFFICULTIES AND OBJECTIONS 131 tho whole of tho sixth and seventh chapters of tho last edition of 1'/te Origin of QJecie ·, in which those and many other cases arc discussed in considerable detail. Useless o1· non-adaptive Characte1'S. Many naturalists seem to be of opinion that a considerable number of the characters which distingnish species arc of no service whatever to their possessors, and therefore cannot have been produced or increased by natural selection. Professors Bronn and Broca have urged this objection on the contincr.t. In America, Dr. Cope, the well-known palreontologist, has long since put forth tho same objection, declaring that non-adapti vo characters arc as numerous as those which are adaptive ; but he differs completely from mo. t who hold the same general opinion in considering that they occur chiefly "in the characters of the classes, orders, families, and other higher groups;" and the objection, therefore, is quite distinct from that in which it is urged that "specific characters " arc mostly useless. More recently, Professor G. J. Romanes bas urged this difficulty in his paper on "Physiological Selection" (Jo~tm. Linn. Soc., vol. xix. pp. 338, 344). He says that the characters "which serve to distinguish allied species arc frequently, if not usually, of a kind with which natural selection can have had nothing to do," being without any utilitarian significance. Again he speaks of "the enormous number," and further on of " the innumerable multitude" of specific peculiarities which arc useless; and he finally declares that tho question needs no further arguing, "because in tho later editions of his works Mr. Darwin freely acknowledges that a large proportion of specific distinctions must be conceded to ue useless to tho species presenting them." I have looked in vain in Mr. Darwin's works to find any such acknowledgment, and I think Mr. Romancs has not sufficiently distinguished between " useless characters " and "useless specific distinctions." On roforri11g to all the passages indicated by him I find that, in regard to specific characters, Mr. Darwin is very cautious in admitting inutility. His most pronounced "admissions" on this question arc the following: "But when, from the nature of the organism and of the conditions, modifications have been induced which are |