The student, however, must always remember that while the study of genius and exceptionable talent is highly interesting, and even, as is quite probable, not without significance for the general laws of heredity, still we must beware of too hastily drawing conclusions from it to bear on the practical questions of eugenics. Genius is rare--and, in a certain sense, abnormal. Laws meant for application to the general population must be based on a study of the general population. Vaerting, himself, realized how inadequate it was to confine our study to cases of genius. Another investigator, Marro, an Italian scientist, in his well-known book on puberty which was published several years ago, brought forth some interesting data showing the result of the age of the parents on the moral and intellectual characters of school-children in Northern Italy. He found that children with fathers below twenty-six at their birth showed the maximum of bad conduct and the minimum of good; they also yielded the greatest proportion of children of irregular, troublesome, or lazy character, but not of really perverse children--the latter being equally distributed among fathers of all ages. The largest number of cheerful children belonged to the young fathers, while the children tended to become more melancholy with ascending age of the fathers. Young fathers produced the largest number of intelligent, as well as of troublesome children; but when the very exceptional intelligent children were considered separately, they were found to be more usually the offspring of elderly fathers. As regarded the mothers, Marro found that the children of young mothers (under twenty-one) are superior, both as regards conduct and intelligence, though the more exceptionally intelligent children tended to belong to more mature mothers. When the parents were both in the same age-groups, the immature and the elderly groups tended to produce more children who were unsatisfactory, both as regards conduct and intelligence--the intermediate group yielding the most satisfactory results of this kind.