=D. Sex Differences.=--Boys differ from girls in the predominance of certain instincts, interests, and mental powers. In boys the fighting instinct, and capacities of leadership, initiative, and mastery are prominent. In girls the instinct of nursing and fondling, and the capacities to comfort and relieve are prominent. These are revealed in the games of the playground. The interests of the two sexes are different, since their games and later pursuits are different. In a system of co-education it is impossible to take full cognizance of this fact in the work of the school. Yet it is possible to make some differentiation between the work assigned to boys and that assigned to girls. For instance, arithmetical problems given to boys might deal with activities interesting to boys, and those to girls might deal with activities interesting to girls. In composition the differentiation will be easier. Such a topic as "A Game of Baseball" would be more suitable for boys, and on the other hand "How to Bake Bread" would make a stronger appeal to girls. Similarly in literature, such a poem as _How They Brought the Good News from Ghent to Aix_ would be particularly interesting to boys, while _The Romance of a Swan's Nest_ would be of greater interest to girls. As to mental capacities, boys are usually superior in those fields where logical reasoning is demanded, while girls usually surpass boys in those fields involving perceptive powers and verbal memory. For instance, boys succeed better in mathematics, science, and the reflective phases of history; girls succeed better in spelling, in harmonizing colours in art work, in distinguishing fine shades of meaning in language, and in memorizing poetry. The average intellectual ability of each sex is nearly the same, but boys deviate from the average more than girls. Thus while the most brilliant pupils are likely to be boys, the dullest are also likely to be boys. It is a scientific fact that there are more individuals of conspicuously clever mind, but also more of weak intellect, among men than there are among women. =A Caution.=--While it has been stated that the teacher should take notice of individual differences in his pupils, it may be advisable also to warn the student-teacher against any extravagant tendency in the direction of such a study. A teacher is occasionally met who seems to act on the assumption that his chief function is not to educate but to study children. Too much of his time may therefore be spent in the conducting of experiments and the making of observations to that end. While the data thus secured may be of some value, it must not be forgotten that control of the subject-matter of education and of the method of presenting that subject-matter to the normal child, together with an earnest, enthusiastic, and sympathetic manner, are the prime qualifications of the teacher as an instructor. APPENDIX SUGGESTED READINGS FROM BOOKS OF REFERENCE CHAPTER I