[76] _Nature_, November 28th, 1907, p. 78. Most biologists from time to time betray the fact that their minds can only be relieved from an intolerable burden, in accounting for the numberless adaptations in organisms, by the view that many of them originate through factors of use and stimuli from environment, and at first are entirely indifferent as regards the survival or better mating of their possessors. To which the stern opponent replies, “What is there to show that in the existing scheme of things there is any provision made which will minister relief to the burden of your little mind?” To which, “answer came there none,” except a subdued reflection that everything we see of living, striving nature around us has a most provoking way of speaking to us of daily, hourly and incessant action and reaction, stimulus and response, and that those who view the process thus do seem to bring some order into what would otherwise be chaos--and yet all the while someone is being grossly deceived! This “may be magnificent but it is not proof,” some will say, and will ask if the older observers of the heavenly bodies were not wrong in their complete conviction that the sun went round the earth. This digression introduces the role of the fly-shaker. If I am told that this muscular sheet in a cow or horse to-day is a relic of raw material inherited from a remote ungulate stock little evolved, and that it contributes in hot weather in the time of flies to the comfort and better mental state of the cow or horse, that it shall be able to keep those enemies at bay, and that the muscle is kept well in order by two or three months’ practice in each year I can understand in a measure its presence to-day. It has an efficient ally in the sweeping tail of a cow and that of a wild horse, and both of these weapons are further aided by the mobile ears of cow and horse, and the stretching movements of its head and neck. Thus the body of a cow, for example, is like a map with four territories delimited, that of the fly-shaker, the tail, the ears and the head and neck. Between these offensive weapons a cow is better defended against flies than a European in India by his punkah, or China was by its great wall, or Britain by the wall of _Vallum_ of Hadrian or the wall of Severus, which with forts and garrisons was designed to protect it. Speaking in allegory the evolving brain of an early ungulate occupies the position of an ancient Chinese Emperor or a Roman Proconsul in Britain in its provision against “barbarians,” either Asiatic or Celtic. The resemblance goes further, for no experienced Roman General, whatever the Celestial minds in China may have thought, would fear that the loss of a sector of his wall would imperil the army of occupation in Britain or the fabric of the Roman Empire. But as, in the long run it contributes to one’s welfare to be comfortable, and even the domestic ungulate is somewhat of a hedonist, a well-developed