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30 of this correspondence. Commencing with the lowest types of life, Mr. Spencer, in successive chapters, traces up this relation of correspondence as extending in space and time, as increasing in specialty, in generality, and in complexity. It is also shown that the correspondence progresses from a more homogeneous to a more heterogeneous form, and that it becomes gradually more integrated—the terms here employed, in respect to the Evolution of mind, being the terms subsequently used in treating of Evolution in general. In the fourth part of the work, under the title of "Special Synthesis," the Evolution is traced out under its concrete form from reflex action up through instinct, memory, reason, feelings, and the will. Mr. Spencer here distinctly avowed his belief that "Life, in its multitudinous and infinitely varied embodiments, has arisen out of the lowest and simplest beginnings, by steps as gradual as those which evolve a homogeneous microscopic germ into a complex organism"—dissent being, at the same time, expressed from that version of the doctrine put forth by the author of the "Vestiges of the Natural History of Creation." It was, moreover, shown by subjective analysis how intelligence may be resolved, step by step, from its most complex into its simplest elements; and it was also proved that there is "unity of composition" throughout, and that thus mental structure, contemplated internally, harmonizes with the doctrine of Evolution.

It was at this time (1854), as I have been informed by Mr. Spencer, when he had been at work upon the "Principles of Psychology" not more than two months, that the general conception of Evolution in its causes and extent, as well as its processes, was arrived at. He had somewhat earlier conceived of it as universally a transformation from the homogeneous into the heterogeneous. This kind of change which Von Baer had shown to take place in every individual organism, as it develops, Mr. Spencer had already traced out as taking place in the progress of social arrangements, in the development of the sciences, and now in the Evolution of mind in general from the lower forms to the higher. And the generalization soon extended itself so as to embrace the transformations undergone by all things inanimate as well as animate. This universal extension of the idea led rapidly to the conception of a universal cause necessitating it. In the autumn of 1854, Mr. Spencer proposed to the editor of the Westminster Review to write an article upon the subject under the title of "The Cause of all Progress," which was objected to as being too assuming. The article was, however, at that time agreed upon, with the understanding that it should be written as soon as the "Principles of Psychology" was finished. The agreement was doomed to be defeated, however, so far as the date was concerned, for, along with the completion of the "Psychology," in July, 1855, there came a nervous break-down, which incapacitated Mr. Spencer for labor during a period of eighteen months—the whole work having been written in less than a year.