No single piece of organic mechanism is oftener or more confidently appealed to by Theists as rendering conclusive evidence on their side than the eye, nor would they run much risk by allowing sentence to go for or against them according as Mr. Darwin has or has not succeeded in his attempt to explain that evidence away. Possibly he may disclaim having made any attempt of the kind, and I must admit that it is less by what he says than by what he leaves unsaid, that he lays himself open to the charge. Indeed, in almost all he says on the subject, I myself cordially agree, embracing even some of his views with less of hesitation than he seems to have felt in putting them forward. He seems to me, for instance, to have somewhat gratuitously admitted it to be apparently 'in the highest degree absurd to suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection.' For since, as he proceeds unanswerably to argue, 'numerous gradations, from an imperfect and simple eye to one perfect and complex, each grade being useful to its possessor, can certainly be shown to exist;' since, as certainly, slight variations of the eye do occur, and are inherited, and since of these variations there cannot but be some which are useful to the animal exhibiting them under changing conditions of life, the difficulty of believing in the formation of a perfect and complex eye by natural selection can be little else than a prejudice of the imagination. He proceeds to indicate some probable stages in the assumed process. Some of the lowest organisms, in which no trace of nerves can be detected, are known to be sensible to light, owing, probably, to the presence in the _sarcode_ of which they are mainly composed, of certain elements which, in organisms somewhat higher in the scale, become aggregated and developed into nerves specially endowed with the same sensibility. An optic nerve thus formed, surrounded by pigment cells, and covered by translucent skin, is the simplest organ that can be called an eye, but it is an eye incapable of distinct vision, and serving only to distinguish light from darkness. In certain star-fishes, small depressions in the layer of pigment-cells are filled with transparent gelatinous matter projecting with a convex surface like a rudimentary cornea, and this, it has been suggested, may serve, not only to form an image, but to concentrate the luminous rays. In insects, the numerous facets in the cornea of their great compound eyes have now been ascertained to form true lenses, the cones, moreover, having been discovered to include curiously modified nervous filaments. It is impossible not, in this series of changes, to perceive the appearance of graduation, nor ought there to be much difficulty in