And its import is in large degree psychological. If we watch a young puppy or kitten learning gradually to deal effectively with some difficulty in its extending environment, we see that it puts forth its efforts at first in a somewhat random and indefinite fashion. It is one of those animals in which intelligence has been evolved to supersede and become the more plastic substitute for instinct. The random and indefinite movements, are in detail reflex responses to stimuli. But whereas, in a piece of highly elaborated instinctive behaviour, such reflexes are grouped into a whole which is co-ordinated through inherited nervous mechanism; in the case of the acts of the puppy or kitten they have to be further co-ordinated, or more elaborately grouped, through experience. To act in one way some of the reflexes have to be checked as redundant and not to the point: to act in another way other reflexes have to be similarly checked; and in a third way, yet others. But in all three some of the reflexes are utilized to different ends. Many conscious situations contain common elements; and this tends to give unity to the developing experience. But they contain also elements and groupings which afford that diversity without which conscious behaviour could not be accommodated to them. So that we have here the conditions under which what is technically termed “the concomitant differentiation and integration of experience” can proceed. And if we speak of the instinct of experimentation we must remember that what we are dealing with is rather an innate tendency or instinctive propensity than a definite and relatively clean-cut piece of instinctive behaviour. It comprises a great number of inherited reflex acts, and may perhaps be fairly called instinctive in detail. But experimentation must be regarded rather as the proximate end of a conative tendency, or group of conative tendencies, whose ultimate biological end is success in dealing with the environment in the sterner struggle for existence during adult life. The tendency is inherited, and therefore falls under the head of instinctive propensity. But “experimentation” is a group-term under which we comprise the general drift of varied modes of behaviour, founded indeed on a congenital basis, but receiving its stamp and character from what is acquired in the course of the experience it provides. It is essentially a process whereby the conscious situations acquire what Dr. Stout terms meaning; and is specially interesting as affording an example of the way in which intelligence moulds and refashions a number of disconnected reflex responses. And if, following Professor Groos, we call it play, it is a little difficult to see how it can be brought in line with his statement[131] that “the play of youth depends on the fact that certain instincts, especially useful in preserving the species, appear before the animal seriously needs them.” Does experimentation occur before it is needed in the economy of animal