Now fill a rectangular glass bowl with water. Across the center place a transparent glass partition, as much shorter than the width of the bowl as will leave a narrow passage at each side. Into one side of the bowl drop a bit of food; drop into the other side some lowly organism, as simple as possible,—say paramecium. Observe it under the microscope. It moves directly towards the food; it strikes the glass partition; it retreats in a straight line; apparently it is a machine. But suddenly it veers slightly about; then it sets out again, at an angle, and once more strikes the glass. It rebounds^ and veers, and strikes again. It re- bounds, and veers, and passes through the opening to the food. There is nothing in the make-up of any machine, nothing in the principles of mechanics, that will explain this judicious veering about, this appearance of directive purpose in the lowest animals known to man.
—Will Durant, The Mansions of Philosophy, page 89.
