Birds have many familiar courtship arts which are hereditary (the isolated adult bird displays almost as much capacity in this direction as does one reared with his kind), but mammals exhibit much less of it. In relation to man there is a theory that sex grounds all art (of this we shall speak later), but a scientific system of comparative courtship of the various human races does not exist; nor, indeed, have we systematic observations of any one people. It is therefore impossible to affirm whether there are such things as instinctive gestures, expressions, caresses, etc., which all human beings recognise as sexual stimuli. From the little that is known it seems probable that the number of such tokens is not great—even the kiss is by no means general! We can only be sure of a universal tendency to approach and to touch one another, and of a disposition to self-exhibition and coquetry as probably instinctive and of the special forms which these tendencies take under the influence of imitation and tradition as secondary causes. Caressing contact may then be regarded as a play when it is an end in itself, which is possible under two conditions: First, when the pursuance of the instinctive movements to their legitimate end is prevented by incapacity or ignorance; and, second, when it is prevented by an act of will on the part of the participants. Children exhibit the first case, adults often enough the second. It is generally known that children are frequently very early susceptible to sexual excitement, and show a desire for contact with others as well as enjoyment of it, without having the least suspicion of its meaning. Keller gives a beautiful and touching example of this in his Romeo und Julia auf dem Dorfe: “On a tiny plot of ground all covered with green herbs the little lass lay down upon her back, for she was tired, and began to croon some words in a monotonous way, while the boy sat near her and joined in the song, almost wishing to follow her example, so weary and languid he felt. The sun shone into the open mouth of the singing girl, gleaming on her teeth so dazzlingly white and shining through the full red lips. The boy noticed this, and taking her head in his hands he examined the little teeth curiously and cried, ‘Guess how many teeth you have?’ She reflected for a moment, as though making a careful calculation, and then said with conviction, ‘A hundred.’ ‘No; thirty-two,’ he answered; ‘but wait till I count again.’ Then he counted aloud, but as he did not make thirty-two he had to begin over several times. The little girl kept still for some time, but as the zealous enumerator seemed never to get any nearer the end of his task she shook him off at last and cried, ‘I will count yours.’ So the boy stretched himself on the grass with the girl above him, throwing his head back while she counted 1, 2, 7, 5, 2; but the task was too hard for the little beauty, and the boy had to teach and