the ultimate cause of force, this relation lies outside the domain of science.
But, admitting this chasm which cannot be bridged—admitting the distinctness of psychology and physiology, a distinctness far greater than exists between any other two departments of science—still there can be no doubt that the changes in the brain and in the mind correspond with each other in the strictest manner. There can be no doubt that we have here two parallel series running side by side with corresponding terms, and that every change in the terms of one series is associated with a change in the corresponding terms of the other series. Whichsoever we take as cause, and whichsoever as effect, the correspondence is undoubted. This much seems certain, and this is sufficient to show that a knowledge of the terms of one series must throw light on the order of succession in the terms of the other series. In a word, physiology, as the simpler and more fundamental science, must form the only true basis of a scientific psychology.
Again, as anatomy only became scientific by becoming comparative anatomy, i. e., by the study of the structure of organisms in their relation to each other, or as connected by the law of evolution; as physiology, too, only became really scientific by becoming comparative physiology; i. e., by tracing the gradual evolution of organic functions; even so psychology can never assume the rank of a science until it becomes comparative psychology; i. e., until it adopts the comparative method, until it studies the different grades and kinds of mentality in their relation to each other, and connects them all by the law of evolution.
So much I have thought it necessary to say in order to show the importance of my subject, and its close connection with physiology. I now pass on to the subject itself.
It is well known that many of the lower animals, especially certain species of insects, perform acts perfectly adapted to accomplish results, and that without previous experience and without instruction. Often the results attained are of a very complex character; results which could not be attained by ourselves except by the exercise of high intelligence, aided by much experience. The extraordinary capacity by which these results are reached with such unerring certainty is called instinct.
I need hardly refer you to examples: You are all familiar with the wonderful instinct of the common honey-bee; their organized communities with perfect division of labor, the precision with which they make their honey-cells on perfect mathematical principles, the honors paid to their queen, their care of her eggs, their wise distribution of food to the larvæ, both its quality and quantity, and the form and size of the containing cells being varied according to the function and even to some extent determining the character of the perfect insect, whether drone, or queen, or worker. You are already familiar with
