At the same time I gladly allow that other modes of observation are possible and in their way useful. This applies to older children who pass into the collective existence of the school-class. Here something like collective or statistical inquiry may be begun, as that into the contents of children's minds, their ignorances and misapprehensions about common objects. Some part of this inquiry into the minds of school children may very well be undertaken by an intelligent teacher. Thus it would be valuable to have careful records of children's progress carried out by pre-arranged tests, so as to get collections of examples of mental activity at different ages. More special lines of inquiry having a truly experimental character might be carried out by experts, as those already begun with reference to children's "span of apprehension," _i.e._, the number of digits or nonsense syllables that can be reproduced after a single hearing, investigations into the effects of fatigue on mental processes, into the effect of number of repetitions on the certainty of reproduction, into musical sensitiveness and so forth. Valuable as such statistical investigation undoubtedly is, it is no substitute for the careful methodical study of the individual child. This seems to me the greatest desideratum just now. Since the teacher needs for practical reasons to make a careful study of individuals he might well assist here. In these days of literary collaboration it might not be amiss for a kindergarten teacher to write an account of a child's mind in co-operation with the mother. Such a record if well done would be of the greatest value. The co-operation of the mother seems to me quite indispensable, since even where there is out-of-class intercourse between teacher and pupil the knowledge acquired by the former never equals that of the mother. FOOTNOTES: [1] The great advantage which the female observer of the infant's mind has over her male competitor is clearly illustrated in some recent studies of childhood by American women. I would especially call attention to a study by Miss M. W. Shinn, (University of California series) _Notes on the Development of a Child_ (the writer's niece), where the minute and painstaking record (e.g. of the child's colour-discrimination and visual space exploration) points to the ample opportunity of observation which comes more readily to women. [2] "Mental Development in the Child and the Race," chap. III. TWINS, THEIR HISTORY AS A CRITERION OF THE RELATIVE POWERS OF NATURE AND NURTURE FRANCIS GALTON [Francis Galton, a cousin of Charles Darwin, has won eminence by bringing problems of human development to the test of statistical inquiry. Among his works are "Hereditary Genius," "English Men of Science, Their Nature and Nurture," "Human Faculty," and "Natural Inheritance." The study of Twins here presented is taken from "Human Faculty," published by Macmillan & Co., London, 1883.]