[102] It is regrettable that Preyer does not describe with some precision the sounds produced by his boy on the twenty-third day. [103] Miss Shinn insists that the laugh did not develop out of the chuckle, since apparently it appeared, as many articulate sounds appear, with something of a sudden completeness. But this is just what we should expect if the laugh is an inherited movement. [104] _Op. cit._, p. 197. [105] Preyer puts this at the end of the first half-year, which seems to me to be late. [106] _Op. cit._, p. 96. [107] On the point of the priority of the smile in the process of evolution see Th. Ribot, _La Psychologie des Sentiments_, p. 346. [108] Darwin, _Expression of the Emotions_, p. 133. [109] A. Lehmann, in his interesting account of the development of the emotions and their expression in the individual, suggests that the first imperfect smile of the infant, which expresses the pleasure of sweetness, is genetically related to the movements of sucking (_Hauptgesetze des menschl. Gefühlslebens_, ss. 295, 296). [110] Darwin, _Expression of the Emotions_, pp. 134, 135. [111] As pointed out above, the French _e_ sound seems to be the common one in children’s laughter. Preyer tells us that the corresponding sound in German (_ä_) occurs in the first infantile babble (_Development of Intellect_, p. 239). [112] _Expression of the Emotions_, pp. 132–3. [113] See the article already quoted on “The Psychology of Tickling, Laughing,” etc., p. 33. [114] See the article already quoted. [115] Dr. Robinson considers that another agreeable effect of tickling may be an inherited echo of the caresses of man’s progenitors. [116] Stanley Hall also suggests that the most ticklish parts, which, according to his inquiries, are _the sole of the foot_, the throat, etc., are the “most vulnerable”. But he does not explain what he means by vulnerable here, and certainly does not appear to use the word in the sense given it by Dr. L. Robinson. [117] Groos deals with the teasing of animals under the head of “Fighting Plays” (_Play of Animals_, p. 136 ff.). [118] H. M. Stanley, _Psychological Review_, 1899, p. 87. [119] This idea, that when we laugh at ludicrous things the process is fundamentally analogous to that of being tickled, has been made the basis of a curious and suggestive physiological theory of laughter, developed by a German writer. See Ewald Hecker, _Die Physiologie und Psychologie des Lachens und des Komischen_. [120] _Loc. cit._, p. 39. [121] I am indebted for this fact to Dr. L. Hill. I believe a like remark applies to all the laughter of play. [122] The nature of the process of emotional development is more fully treated, and the relation of its effect to that of the dulling action of repetition is indicated, in my work, _The Human Mind_, vol. ii., p. 75 ff.