that mentality is the effect. The brain is an indispensable condition, but, to use the language of Hering, "I do not say cause, for this I do not know." It is not for psychology to assert whether mind or matter gives rise to the other or which constitutes reality. These rocks are chiefly on the side which epistemology is to tunnel. Back in the twilight of existence the biologists find that they possibly may exist together, although at what time in the chain of being consciousness is found there is no consensus of opinion. Certainly in very low stages of life, mind and matter are associated; and as we ascend the scale of being to man we find them apparently varying alike in volume and power.23 I assume, then, a condition which I shall designate as genetic parallelism. By this is meant that in the successive stages of development the two phenomena are found parallel, and also that psychology cannot state which gives rise to the other. I further posit functional interaction as the theory which, upon the whole, best conforms to the many facts observed in this and previous chapters. Putting the two together, the hypothesis which most strongly appeals to me as the one best able to harmonize the mass of data considered may be styled Genetic Parallelism and Functional Interaction. At the beginning

23 Not absolute increase in brain weight, but the proportionate increase of the size of the brain to the body is

meant.

of the next chapter a schematic outline will be given to illustrate the manner in which I conceive that this relation may exist. Assuming that the phenomena are genetically parallel, no attempt will be made to inquire into the reality of either phenomenon or its genesis. These are ontological and metaphysical questions. I shall only attempt to illustrate briefly a possible functional relation which has been inferred from the data accumulated in the first four chapters.

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