If the above be a correct statement of the facts, and I believe it is, it follows that the brain is the medium or laboratory in which thoughtful reasoning and the higher mental phenomena are generated. As a corollary to this important deduction we expect the amount and quality of mental activities to be proportionate to the size of the cerebral organ. There is some latent truth in this idea, but in drawing definite conclusions of this nature from the actual bulk of brain substance there are some modifying influences to be considered. The actual bulk of an elephant's brain is about three times that of man. In making comparisons of this kind we must consider the relative size of the brain to the animal's body, and, above all, the quality of the brain cells, and no doubt many other factors. But for the present purpose we have only to deal with the brains of the anthropoid apes, and compare them with that of man. On this point Dr Thomson thus writes : —
So far, we have included man in our observations on animal life, but now we come to the parting of their ways. The real problem which now confronts us is to account for the existence of man's large brain under the influence of existing cosmic forces. But before propounding any solution of the problem, it is advisable to bring into focus the discursive observations which I have laid before you, so that you may better realise where we are and what we are driving at.
Retrospect.
Glancing through the aeons that have rolled past since life began on the globe, we have seen how myriads of generations