BRITISH WARBLERS
to reduce the emotional behaviour of the group to some order rather than a definite contribution to our knowledge of the subject. Why do I attribute a certain level of emotional development to such and such a species? Knowing, as we do, that in the case of human emotion a stimulus of an appropriate kind is necessary to produce a definite response, we can scarcely doubt that the same is true of the primary emotions of the lower animals. And since all knowledge of the emotion of a bird, in its subjective aspect, is beyond human understanding, how can we be sure that the comparisons are made under corresponding conditions, and are we therefore justified in even attempting to decide as to the relative position this and this species ought to occupy in any scale of emotion? I grant the difficulty, and even admit that the same individual does not always respond actively when under the influence of sexual or parental emotion. Perhaps my conclusions may be said to be based more upon impressions gained from a long acquaintance with the different species, than upon anything in the nature of tangible fact. And yet extravagant antics, which comprise an outstretching, flapping, and fluttering of wings, a spreading and raising of the tail, peculiar contortions of the body, and an equally peculiar employment of the vocal powers, are surely sufficient reason for assigning to the actor a different level in an emotional scale from one whose movements attract but little attention or excite but little wonder. Starting thus with the two extremes I have allotted the intermediate places as they seemed to me to be merited. The extremes may consequently be said to be based upon actual evidence, the intermediate stages being in some measure impressionist, though I hope not altogether so.
The similarity of the motor reactions at different emotional periods next requires consideration; it is a possible line of investigation from which something may come. The perceptual powers of animals are probably greater than we imagine. We think that we discern similarity in the behaviour arising in wholly different situations, yet some
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