Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/210

160 image, and special arrangements for the accommodation of the eye to distances. By glancing, therefore, at different animals, we see the eye in different stages of perfection. But the gradual development of the eye of man offers a series of transitional stages, which are permanently represented by the eyes of the lower animals. Now, if the eye has gradually been perfected through the Survival of the Fittest, we understand why the transitional stages in the development of the eye of man have permanent representatives in the eyes of the lower animals; but if the eye has been created for the purpose of seeing, we neither understand why such an extraordinary method is adopted in its formation nor why it is not a perfect optical instrument. The same reasoning will apply to the human ear as well as to the eye, they both beginning as depressions in the skin, which later, closing, form the primitive eye and ear vesicles.

We tried to show in the chapters on Zoology, Botany, Geology, and Embryology, that the structure of plants and animals, their petrified remains, and their manner of development, are explained by supposing that life has evolved, that there has been a gradual development of the higher form? of life from the lower, accompanied here and there by a retrograding metamorphosis. In the early part of this chapter we called attention to the facts of Geographical Distribution not being consistent with a theory that supposed plants and animals had been created for special localities, but that they could be explained by supposing that life migrated from place to place, being more or less modified from time to time by the new conditions of existence, natural barriers being often the cause of the great difference exhibited by plants and animals living under similar conditions. The conclusion of an Evolution of Life,