Higher up in the cortex, or convoluted envelope of the brain, come the areas for hearing and seeing, the latter being the more extensive. These areas are filled mainly by a great number of sensory nerve-centres or cells, connected with one another in a very complicated network. These seem to be connected with the multitude of ideas which are excited in the brain by perceptions derived from the higher senses, especially that of sight. The simple movements are produced by a few large motor-centres, which have only one idea and do only one thing, whether it be to move the leg or the arm. But a sensation from sight often calls up a multitude of ideas. Suppose you see the face of one with whom some fifty years ago you may have had some youthful love passages, but your lives drifted apart, and you now meet for the first time after these long years, how many ideas will crowd on the mind, how many nerve-cells will be set vibrating, and how many nerve-currents set coursing along intricate paths! No wonder that the nerve-corpuscles are numerous and minute, and the nerve-channels many and complicated. When we come to the seats of the intellectual faculties the question becomes still more obscure. They are probably situated in the hinder and front parts of the surface of the brain, and depend on the grey matter consisting of an immense number of minute sensory cells. It has been computed that there are millions in the area of a square inch, and they are all in a state of the most delicate equilibrium, vibrating with the slightest breath of nervous impression. They depend for their activity entirely on the sensory perceptive centres, for there is no consciousness in the absence of sensory stimulation, as in dreamless sleep. Perception, however caused, whether by outward stimulation of real objects, or by former perceptions revived by memory, sends a stream of energy through the sense-area, which expands, like a river divided into numerous channels, fertilising the intellectual area, where it is stored up by memory, giving us the idea of continual individual existence, and by some mysterious and unknown process becoming transformed into consciousness and deliberate thought. And conversely the process is reversed when what we call will is excited, and the small currents of the intellectual area are concentrated by an effort of attention and sent along the proper nerve-channels to the motor-centres, whose function it is to produce the desired movement. This mechanical explanation, it will be observed, leaves entirely untouched the question of the real essence and origin of these intellectual faculties, as to which we know nothing more than we do of the real essence and origin of life, of matter, and of energy.