Origin of Species Variorum

He who will go thus far, ought not to hesitate to go one step further, if he finds on finishing this volume that large bodies of facts, otherwise inexplicable, can be explained by the theory of descent with modification; he ought to admit that a structure even as perfect as ... an eagles eye might be formed by natural selection, although in this case he does not know .. the transitional states. It has been objected that in order to modify the eye and still preserve it as a perfect instrument, many changes would have to be effected simultaneously, which, it is assumed, could not be done through natural selection; but as I have attempted to show in my work on the variation of domestic animals, it is not necessary to suppose that all the modifications were simultaneous, if they were extremely slight and gradual. ↑ Even in the ... most highly organised division of the animal kingdom, namely the Vertebrata, we can start ... from an eye so simple, that it consists, as in the lancelet, of a little .. sack of transparent skin, furnished with a nerve and lined with pigment, but destitute of any other apparatus. .. .. .. .. .. .. In both fishes and reptiles, as Owen has remarked, "the range of gradations of dioptric structures is very great." It is a significant fact that even in man, according to the high authority of Virchow, the beautiful crystalline lens is .. formed in the embryo by an accumulation of epidermic cells, lying in a sack-like fold of the skin; and the vitreous body is formed from embryonic sub-cutaneous tissue. It is indeed indispensable, in order to arrive at a just conclusion regarding the formation of the eye, with all its marvellously perfect characters, that the reason should conquer the imagination; but I have felt this difficulty far too keenly to be surprised at any degree of hesitation in extending the principle of natural selection to so startling