In order to understand the causes which bring about these alterations of type, it is necessary to know how long a time must have elapsed since the immigration of the parents before a noticeable change of type of the offspring is brought about. This investigation has been carried out mainly for the cephalic index, which, during the period of growth of the individual, undergoes only slight modifications. The investigation of the Hebrews shows very clearly that the cephalic index of the foreign-born is practically the same, no matter how old the individual at the time of immigration. This might be expected when the immigrants are adult or nearly mature; but it is of interest to note that even children who come here when one year or a few years old develop the cephalic index characteristic of the foreign-born. This index ranges around 83. When we compare the value of this index with that of the index of the American-born, according to the time elapsed since their immigration, we find a sudden change. The value drops to about 82 for those born immediately after the immigration of their parents, and drops to 79 in the second generation; i.e., among the children of American-born children of immigrants. In other words, the effect of American environment makes itself felt immediately, and increases slowly with the increase of time elapsed between the immigration of the parents and the birth of the child. The conditions among the Sicilians and Neapolitans are quite similar to those observed among the Hebrews. The cephalic index of the foreign-born remains throughout on almost the same level. Those born in America immediately after the arrival of their parents show an increase of the cephalic index. In this case, the transition, although rapid, is not quite so sudden as among the Hebrews, probably because among those born a year before or after immigration there is some doubt as to the place of their birth. These uncertainties are due to the habit of the Italians to migrate back and forth between Italy and America before finally settling here, and to the indefiniteness of their answers in regard to the places of birth of the child, which sometimes had to be inferred from the age of the child and the year of immigration of the mother. As long as this uncertainty exists, which is hardly present at all in the data relating to the Hebrews, it does not seem necessary to assume any other cause for the more gradual change of the cephalic index about the time of immigration. The Italian immigration is so recent, that individuals who were born many years after the arrival of their parents in America are very few in number, and no individuals of the second generation have been observed. For this reason it is hardly possible to decide whether the increase of the cephalic index continues with the length of time elapsed between the immigration of the parents and the birth of the child.