R’s teacher[17] writes of him, “His ability in academic work seems well distributed, though strongest in mathematics. For this grade he is remarkably low in art and industrial work, but he would be average in the second grade, where his age would usually place him. His artistic feeling is all for music and literature.... I think he is rather clumsy with his hands even for his age, though not much below the average child. With his mental ability he can learn to do anything in which his interest is aroused.... As he goes on, I hope that we can arrange for him to work with more advanced groups in mathematics and science, though remaining in the present group for most of the day.... In mathematics it is noticeable that although he can use short cuts which are Greek to the class, he is quite as apt to make an error in concrete problems as the other bright children. This is not lack of attention or interest, for he is always keenly alive in any lesson in mathematics. For example, in shop where he was making a table with a top 24 inches square, he was shown the lumber (12 inches wide) and asked how many pieces he must prepare for the table. He replied ‘three,’ and it was some time before he was led to recognize his mistake.” [Illustration: FIG. 17.—Showing R’s calculation on Test 2, Army Alpha, Form 5, at the age of 7 years 6 months, five minutes being allowed for the performance. Note immature formation of the numerals. The only part of the figuring done on paper appears in the margin. ] [Illustration: FIG. 18.—Showing R’s calculation on Test 6, Army Alpha, Form 5, at the age of 7 years 6 months, three minutes being allowed for the performance. Note immature formation of the numerals. ] With his love of mathematics, R combines a passion for classifying. As early as his first year of life, he would classify his playing blocks according to the shape of the letters on them,—O, Q, P, and the like together, and A, V, W, N, M, and the like in another group, and so forth. This delight in classifying is also one of D’s most conspicuous characteristics. X. THE INHERITANCE OF ARITHMETICAL ABILITIES