Furthermore, he points out the fact that in early periods of the earth the organic forming power which ruled, must have been a higher one than it is at the present time; in like manner as the first period in the embryonic development of individuals is to-day the most productive. This higher power of organization, he says, could consist in a higher power of changing organisms into new species, as well as in a higher power of producing new species through primitive generation; or it could consist in both. In general, there is no reason to suppose that primitive generations which took place at the first origination of life on earth, could not have been repeated later and oftener. The nearer a generation was to these individuals originated through primitive generation, the greater was undoubtedly its flexibility and changeableness; the farther, the greater the fixity of type. [4] After the completion this manuscript, the author found that K. E. von Baer, in his treatise upon Darwin's doctrine, pays especial attention to the change of generation and also to the metamorphosis of plants and animals in exactly the same sense and reaches the same conclusion. [5] Compare Max Mueller, "Lectures on the Science of Language," 6th ed., London, 1871, vol. I, p. 403. [6] Compare v. Baer, "Studies, etc.," p. 294 ff. [7] Darwin says, on page 146, Eng. Ed., of his "Descent of Man": "In the earlier editions of my 'Origin of Species', I perhaps attributed too much to the action of natural selection or the survival of the fittest.... I did not formerly sufficiently consider the existence of structures which, as far as we can at present judge, are neither beneficial nor injurious; and this I believe to be one of the greatest oversights as yet detected in my work.... An unexplained residuum of change, perhaps a large one, must be left to the assumed uniform action of those unknown agencies, which occasionally induce strongly-marked and abrupt deviations of structure in our domestic productions."