In the same diagram (Fig. 5) I have set forth the acceleration-curves in respect of increment of weight for both man and woman, according to Quetelet. That growth in boyhood and growth in girlhood follow a very different course is a matter of common knowledge; but if we simply plot the ordinary curve of growth, or velocity-curve, the difference, on the small scale of our diagrams, {70} is not very apparent. It is admirably brought out, however, in the acceleration-curves. Here we see that, after infancy, say from three years old to eight, the velocity in the girl is steady, just as in the boy, but it stands on a lower level in her case than in his: the little maid at this age is growing slower than the boy. But very soon, and while his acceleration-curve is still represented by a straight line, hers has begun to ascend, and until the girl is about thirteen or fourteen it continues to ascend rapidly. After that age, as after sixteen or seventeen in the boy’s case, it begins to descend. In short, throughout all this period, it is a very _similar_ curve in the two sexes; but it has its notable differences, in amplitude and especially in _phase_. Last of all, we may notice that while the acceleration-curve falls to a negative value in the male about or even a little before the age of thirty years, this does not happen among women. They continue to grow in weight, though slowly, till very much later in life; until there comes a final period, in both sexes alike, during which weight, and height and strength all alike diminish. From certain corrected, or “typical” values, given for American children by Boas and Wissler (_l.c._ p. 42), we obtain the following still clearer comparison of the annual increments of _stature_ in boys and girls: the typical stature at the commencement of the period, i.e. at the age of eleven, being 135·1 cm. and 136·9 cm. for the boys and girls respectively, and the annual increments being as follows: Age 12 13 14 15 16 17 18 19 20 Boys (cm.) 4·1 6·3 8·7 7·9 5·2 3·2 1·9 0·9 0·3 Girls (cm.) 7·5 7·0 4·6 2·1 0·9 0·4 0·1 0·0 0·0 Difference −3·4 −0·7 4·1 5·8 4·3 2·8 1·8 0·9 0·3