II. THE RELATIONSHIPS AMONG CAPACITIES 11 The Coefficient of Correlation. General Intelligence _vs._ Special Aptitudes. Correlation of Abilities in Various Groups. Studies of Disorganizing Minds. Is Intellect Inherited as a Unit? Can an Intellect Be Trained as a Unit? The Hierarchy of Abilities. Present Status of the Problem. Measurement of General Intelligence: The IQ. Measurement of Special Ability. The Psychographic Picture of Individuality. At What Age Is Mental Endowment Evident? The Frequency of Marked Special Talents and Defects. Possible Origin of the Dissociation of Certain Capacities. III. CONSIDERATION OF THE NEURAL BASIS 49 The Physiological Mechanism of Mental Life. Attempted Localization of Mental Functions. Theory of Congenital Lesion or Atrophy Criticized. Regeneration of Function without Regeneration of Structure in Injured Brains. Attempts to Establish a Neural Basis for the “Two Factor Theory” and the “Two Level Theory.” Present Status of the Problem. IV. READING 57 Relation between IQ and Capacity for Reading. The Mechanics of Reading. Comprehension in Reading. Word Blindness. Psychological Studies of Special Defect in Reading. Nervous Instability and Special Defect in Reading. A Four-Year Study of a Non-Reader. Summary of Studies of Non-Readers. Cases of Special Ability in Reading. The Significance of Literacy. V. SPELLING 98 Coherence among Linguistic Functions. Analysis of Learning to Spell. Psychological Examination of Poor Spellers. Can Special Defect in Spelling Be Overcome? Does Reading Teach Spelling? Illustrative Cases. VI. ARITHMETIC 114 Relation between IQ and Capacity for Arithmetic. Distinction between Arithmetic and Mathematics. The Psychology of Arithmetical Calculation. The Organization of Arithmetical Abilities. Psychological Studies of Special Deficiency in Arithmetic. Methods of Detecting Wrong or Incomplete Habits. Nervous Instability and Special Deficiency in Arithmetic. Arithmetical Prodigies. Arithmetical Ability of Two Children of IQ 184 and IQ 187 (Stanford-Binet). The Inheritance of Arithmetical Abilities. Implications for Education.