From the principles laid down in the last sentence it would follow that if man were constructed upon a plan as different from that of any other animal as that of a sea-urchin is from that of a whale, it would be "equally probable" that he had been developed from some other animal as it is now, when we know that for every bone, muscle, tooth, and even pattern of tooth, in man, there is a corresponding bone, muscle, tooth, and pattern of tooth, in an ape. And this shows one of two things--either that the Quarterly Reviewer's notions of probability are peculiar to himself, or that he has such an overpowering faith in the truth of evolution that no extent of structural break between one animal and another is sufficient to destroy his conviction that evolution has taken place. But this by the way. The importance of the admission that there is nothing in man's physical structure to interfere with his having been evolved from an ape is not lessened because it is grudgingly made and inconsistently qualified. And instead of jubilating over the extent of the enemy's retreat, it will be more worth while to lay siege to his last stronghold--the position that there is a distinction in kind between the mental faculties of man and those of brutes, and that in consequence of this distinction in kind no gradual progress from the mental faculties of the one to those of the other can have taken place. The Quarterly Reviewer entrenches himself within formidable-looking psychological outworks, and there is no getting at him without attacking them one by one. He begins by laying down the following proposition. "'Sensation' is not 'thought,' and no amount of the former would constitute the most rudimentary condition of the latter, though sensations supply the conditions for the existence of 'thought' or 'knowledge'" (p. 67). This proposition is true, or not, according to the sense in which the word "thought" is employed. Thought is not uncommonly used in a sense co-extensive with consciousness, and, especially, with those states of consciousness we call memory. If I recall the impression made by a colour or an odour, and distinctly remember blueness or muskiness, I may say with perfect propriety that I "think of" blue or musk; and, so long as the thought lasts, it is simply a faint reproduction of the state of consciousness to which I gave the name in question, when it first became known to me as a sensation.