The decrease in the width of head that has been observed is so large that it cannot be considered simply as an effect of compensation; but we have to make the additional hypothesis that the American-born children lie so much on their sides that a narrowing of the head is brought about by mechanical pressure. The same considerations hold good in all the other types. If, therefore, in one case the greater freedom of position of the child increases the length of its head, it is difficult to see why, among the Bohemians, the same causes should decrease both horizontal diameters of the head, and why, among the Sicilians, the length should decrease, the width increase. The development of the width of the face seems to my mind to show most clearly that it is not the mechanical treatment of the infant that brings about the changes in question. The cephalic index suffers a very slight decrease from the second year to adult life. It is therefore evident that children who arrive in America very young cannot be much affected by American environment in regard to their cephalic index. On the other hand, if we consider a measurement that increases appreciably during the period of growth, we may expect that in children born abroad but removed to America when young, the total growth may be modified by American environment. The best material for this study is presented by the Bohemians, among whom there are relatively many full-grown American-born individuals. The width of face of Bohemians, when arranged according to their ages at the time of immigration, shows that there is a loss among those who came here as young children,—the greater, the younger they were. Continuing this comparison with the Americans born one, two, and more years after the arrival of their mothers, the width of face is seen to decrease still further. It appears, therefore, that the American environment causes a retardation of the growth of the width of face at a period when mechanical influences are no longer possible. I have not carried through the analogous investigation for stature, because in this case the increase might simply be ascribed to the better nutrition of most of the north and central European immigrants after their immigration into this country.