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262 his thoughts. He remarks that he 'can understand the gradation only as a prolonged struggle against unfavorable conditions.'" The President of the Geological Society has said that, "looking at the general mass of Mr. Darwin's results, I can not help considering his voyage around the world as one of the most important events for geology which has occurred for many years." Professor John W. Judd, noticing the works of this series in a group, said, in 1877, "Students of Mr. Darwin's earlier geological writings must all have been impressed by the powers of minute observation, the acumen in testing, and the skill in grouping data, and the boldness and originality in generalization which distinguished their author; for these characteristics are no less distinguished in the theory of coral reefs than in that of natural selection"; and "these 'Geological Observations' are well worthy to take their place in the long series of the author's contributions to the doctrine of descent side by side with those more widely known works on different departments of zoölogy and botany which have been published subsequently to the 'Origin of Species.'

His most important work on zoölogy, "A Monograph of the Family Cirripedia," was published by the Ray Society, 1851 to 1853. It gave accurate determinations of every recognized species of the animals known as barnacles and sea-acorns; and was shortly afterward followed by another monograph on the fossil species of the same family, which was brought out by the Philosophical Society. All of these works—each of which was, as the estimates we have quoted indicate, of the first importance in itself, and each of which is a standard to this day—were but as preliminaries to the culminating achievement of Mr. Darwin's life, the exposition of the doctrine of the origin of species and development by natural selection, as given in the series of works on "The Origin of Species by Means of Natural Selection; or, the Preservation of Favored Paces in the Struggle for Life" (1859); "The Variations of Plants and Animals under Domestication" (1867), and "The Descent of Man and Selection in Relation to Sex" (1871); and in the numerous special works in which he has made various particular phenomena of animal and vegetable life illustrate and re-enforce his great doctrine. The views expressed and defined in these works, although, now that they have "come of age," they have sensibly and profoundly affected the whole world of thought, were a surprise. Scientific men received them hesitatingly or with incredulity; those who were not scientific with displeasure. Yet they were not wholly novel; for Aristotle, Goethe, Mr. Darwin's grandfather, and others, had suggested similar hypotheses, and Mr. Wallace had independently reached conclusions very like those enunciated by Mr. Darwin. They have had to make their way against the prepossessions of the minds to whom they appealed, and against the prejudices which those prepossessions awakened when they were assailed.

Gradually the theory of descent gained acceptance among the