Just as there is a marked difference in “phase” between the growth-curves of the two sexes, that is to say a difference in the periods when growth is rapid or the reverse, so also, within each sex, will there be room for similar, but individual phase-differences. Thus we may have children of accelerated development, who at a given epoch after birth are both rapidly growing and already “big for their age”; and others of retarded development who are comparatively small and have not reached the period of acceleration which, in greater or less degree, will come to them in turn. In other words, there must under such circumstances be a strong positive “coefficient of correlation” between stature and rate of growth, and also between the rate of growth in one year and the next. But it does not by any means follow that a child who is precociously big will continue to grow rapidly, and become a man or woman of exceptional stature. On the contrary, when in the case of the precocious or “accelerated” children growth has begun to slow down, the backward ones may still be growing rapidly, and so making up (more or less completely) to the others. In other words, the period of high positive correlation between stature and increment will tend to be followed by one of negative correlation. This interesting and important point, due to Boas and Wissler[109], is confirmed by the following table:― _Correlation of Stature and Increment in Boys and Girls._ (_From Boas and Wissler._) Age 6 7 8 9 10 11 12 13 14 15 Stature (B) 112·7 115·5 123·2 127·4 133·2 136·8 142·7 147·3 155·9 162·2 (G) 111·4 117·7 121·4 127·9 131·8 136·7 144·6 149·7 153·8 157·2 Increment (B) 5·7 5·3 4·9 5·1 5·0 4·7 5·9 7·5 6·2 5·2 (G) 5·9 5·5 5·5 5·9 6·2 7·2 6·5 5·4 3·3 1·7 Correlation (B) ·25 ·11 ·08 ·25 ·18 ·18 ·48 ·29 −·42 −·44 (G) ·44 ·14 ·24 ·47 ·18 −·18 −·42 −·39 −·63 ·11 {82} A minor, but very curious point brought out by the same investigators is that, if instead of stature we deal with height in the sitting posture (or, practically speaking, with length of trunk or back), then the correlations between this height and its annual increment are throughout negative. In other words, there would seem to be a general tendency for the long trunks to grow slowly throughout the whole period under investigation. It is a well-known anatomical fact that tallness is in the main due not to length of body but to length of limb.