Age 5 6 7 8 9 Stature (Bowditch) 4·76 4·60 4·42 4·49 4·40 Stature (Boas and Wissler) 4·15 4·14 4·22 4·37 4·33 Weight (Bowditch) 11·56 10·28 11·08 9·92 11·04 Age 10 11 12 13 14 Stature (Bowditch) 4·55 4·70 4·90 5·47 5·79 Stature (Boas and Wissler) 4·36 4·54 4·73 5·16 5·57 Weight (Bowditch) 11·60 11·76 13·72 13·60 16·80 Age 15 16 17 18 Stature (Bowditch) 5·57 4·50 4·55 3·69 Stature (Boas and Wissler) 5·50 4·69 4·27 3·94 Weight (Bowditch) 15·32 13·28 12·96 10·40 The result is very curious indeed. We see, from Fig. 11, that the curve of variability is very similar to what we have called the acceleration-curve (Fig. 4): that is to say, it descends when the rate of growth diminishes, and rises very markedly again when, in late boyhood, the rate of growth is temporarily accelerated. We {80} see, in short, that the amount of _variability_ in stature or in weight is a function of the _rate of growth_ in these magnitudes, though we are not yet in a position to equate the terms precisely, one with another. [Illustration: Fig. 11. Coefficients of variability of stature in Man (♂). from Boas and Wissler’s data.] If we take not merely the variability of stature or weight at a given age, but the variability of the actual successive increments in each yearly period, we see that this latter coefficient of variability tends to increase steadily, and more and more rapidly, within the limits of age for which we have information; and this phenomenon is, in the main, easy of explanation. For a great part of the difference, in regard to rate of growth, between one individual and another is a difference of _phase_,—a difference in the epochs of acceleration and retardation, and finally in the epoch when growth comes to an end. And it follows that the variability of rate will be more and more marked, as we approach and reach the period when some individuals still continue, and others have already ceased, to grow. In the following epitomised table, {81} I have taken Boas’s determinations of variability (σ) (_op. cit._ p. 1548), converted them into the corresponding coefficients of variability ((σ/_M_) × 100), and then smoothed the resulting numbers. _Coefficients of Variability in Annual Increment of Stature._ Age 7 8 9 10 11 12 13 14 15 Boys 17·3 15·8 18·6 19·1 21·0 24·7 29·0 36·2 46·1 Girls 17·1 17·8 19·2 22·7 25·9 29·3 37·0 44·8 — The greater variability of annual increment in the girls, as compared with the boys, is very marked, and is easily explained by the more rapid rate at which the girls run through the several phases of the phenomenon.