But the practical value of this method of thinking is, as I say, an arguable point; it is indeed clear that a great immediate advance, especially in non-human biology, has been and may still be made by translating the uncertain and often risky terms of subjective psychology into those based upon the objective description of directly observable behaviour. However, it is equally easy to maintain, and I for one maintain it, that to omit a whole category of phenomena from consideration is unscientific, and must in the long run lead to an unreal, because limited, view of things; and that, when great detail of analysis is not required, but only broad lines and general comparison, the psychological terminology, of memory, fear, anger, curiosity, affection, is the simpler and more direct tool, and should be used to supplement and make more real the cumbersome and less complete behavioristic terminology, of modification of behaviour, fright, aggression, and the rest. It is at least abundantly clear that, if we are to believe in the principle of uniformity at all, we must ascribe emotion to animals as well as to men: the similarity of behaviour is so great that to assert the absence of a whole class of phenomena in one case, its presence in the other, is to make scientific reasoning a farce. “_Pas de cerveau--que de l’âme._” Those especially who have studied birds will subscribe to this. The variety of their emotions is greater, their intensity more striking, than in four-footed beasts, while their power of modifying behaviour by experience is less, the subjection to instinct more complete. Those who are interested in the details can see from experiments, such as those recorded by Mr. Eliot Howard in his _Territory in Bird Life_, how limited is a bird’s power of adjustment; but I will content myself with a single example, one of nature’s experiments, recorded by Mr. Chance last year by the aid of the cinematograph--the behaviour of small birds when the routine of their life is upset by the presence of a young Cuckoo in the nest. When, after prodigious exertions, the unfledged Cuckoo has ejected its foster-brothers and sisters from their home, it sometimes happens that one of them is caught on or close to the rim of the nest. One such case was recorded by Mr. Chance’s camera. The unfortunate fledgling scrambled about on the branches below the nest; the parent Pipit flew back with food; the cries and open mouth of the ejected bird attracted attention, and it was fed; and the mother then settled down upon the nest as if all was in normal order. Meanwhile, the movements of the fledgling in the foreground grew feebler, and one could imagine its voice quavering off, fainter and fainter, as its vital warmth departed. At the next return of the parent with food the young one was dead.