details." From these replies he draws various conclusions, such as that "extreme similarity and extreme dissimilarity between twins of the same sex are nearly as common as moderate resemblance." He says that when twins are a boy and a girl they are never closely alike. In the thirty-five cases of great similarity, there were seven in which both twins suffered from some special ailment or some exceptional peculiarity. They were liable to sickness at the same time in nine out of thirty-five cases. Eleven pairs out of this number were remarkably similar in the association of ideas, making the same remarks on the same occasion. In sixteen cases their dispositions were very similar. He affirms that only a few retain their close resemblance through life, either physically or in disposition. Again, he says that it is a fact that "extreme dissimilarity, such as existed between Jacob and Esau, is a no less marked peculiarity in twins of the same sex than extreme similarity."
Since his views were published I have observed various twins, and have seen some instances of astonishing similarity, but in other children of the same parents, not twins, more instances which could readily be accounted for by heredity and the influence of similar surroundings and nurture. A number of instances could be given of distinguished men, now living or but recently deceased, where the physical and mental resemblances between them and their twin brothers are no greater than ordinarily exist between brothers. Is it not important in a general examination to collect with equal care instances of as great similarities between children who have the same parents but who are not twins? If not, no light can be shed on an extraneous cause. Harmonies of disposition, similarity of personal appearance, and devotion to each other through life have been seen between
