One may hazard the guess that the process may have been something of this kind. The position of the open mouth during a broad smile was, we may reason, in itself favourable to the production of vocal sounds. We may, after the analogy of positions of the eyes, speak of it as the “primary position” of the vocal chamber when opened. This primary position would pretty certainly be specially favourable to the utterance of a certain kind of sound, let us say that commonly indicated by “eh,”[111] together with something of the guttural or chuckling accompaniment of this in the sound of laughter. We may then infer that, when some of the reiterated babble-like sounds were produced during states of pleasurable satisfaction, the same (primary) position would be taken up. We should thus get, as psycho-physical concomitants of the sensed position of the opened mouth during a broad smile or “grin,” not only a disposition to reiterate the “eh” or some similar sound as a completion of the whole action, of which the opening of the mouth is the first stage, but a definite associative co-ordination between the movement of opening the mouth and the reiterated actions of the muscles of the respiratory and vocal apparatus. In this way we may understand how, when the pleasurable state expressed by a smile increased in intensity, as, for example, when the happy feeling excited by the sight of a face passed into the joy of recognising a member of the family, the {175} movements would widen out into those of a laughter-like utterance. It appears to me that, in this connection, the observed course of development of laughter in the individual is not without its suggestiveness. Miss Shinn remarks that Ruth’s mouth was opened wide on the 113th day—five days before the first laugh—while the child was tossed and tumbled. Under date of the 134th day, again, we read of much laughter of an inaudible kind, consisting of broad laughter-like smiles; and these observations certainly show that about the date of the first laughter an expanded smile, indistinguishable from a laugh save by the absence of the respiratory and vocal adjunct, was frequent. In other words, they tell us that about the time when she achieved her first laugh she was freely practising the intermediate facial step between the earlier smile and the true laugh.