Such being my basis of assumption, we began by considering the state of the question _a priori_. If, in accordance with our assumption, the process of organic and of mental evolution has been continuous throughout the whole region of life and of mind, with the one exception of the mind of man, on grounds of an immensely large analogy we must deem it antecedently improbable that the process of evolution, elsewhere so uniform and ubiquitous, should have been interrupted at its terminal phase. And this antecedent presumption is still further strengthened by the undeniable fact that, in the case of every individual human being, the human mind presents to actual observation a process of gradual development, extending from infancy to manhood. For it is thus shown to be a matter of observable fact that, whatever may have been the origin or the history of human intelligence in the past, as it now exists—or, rather, as in every individual case it now comes into existence—it proves itself to be no exception to the general law of evolution: it unquestionably does admit of gradual growth from a zero level, and without such a gradual growth we have no evidence of its becoming. Furthermore, so long as it is passing through the lower stages of this growth, the human mind ascends through a scale of faculties which are parallel with those that are permanently presented by what I have termed the psychological species of the animal kingdom—a general fact which tends most strongly to prove that, at all events up to the time when the distinctively human qualities of ideation are attained, no difference of kind is apparent between human and brute psychology. Lastly, not only in the individual, but also in the race, the phenomena of mental evolution are conspicuous—so far, at least, as the records of the human race extend. Whether we have regard to actual history, to tradition, to antiquarian remains, or flint implements, we obtain uniform evidence of a continuous process of upward development, which is thus seen to be as characteristic of those additional attributes wherein the human mind now surpasses that of any other species as it is of those attributes which it shares with other species. Therefore, if the process of mental evolution was interrupted between the anthropoid apes and primitive man during the pre-historic period of which we have no record, it must again have been resumed with primitive man, after which it must have continued as uninterruptedly in the human species as it previously did in the animal species. This, to say the least, is a most improbable supposition. The law of continuity is proved to apply on both sides of a psychological interval, where there happens to be a necessary absence of historical information. Yet we are asked to believe that, in curious coincidence with this interval, the law of continuity was violated—notwithstanding that in the case of every individual human mind such is known never to be the case.