Contents: Introductory. 1. The Behaviour of the Lower Animals. 2. Behaviour of Insects. 3. Behaviour of the Vertebrates. 4. The Instincts of the Mammals and of Man. 5. Habit and Intelligence in Animals. 6. Behaviour of the Natural Man. 7. Perceptual Thinking. 8. Attention and Interest. 9. Imagining-Anticipating-Recollecting. 10. Emotion. 11. The Derived Emotions. 12. Disposition. 13. Temper. 14. Temperament and Moods. 15. Belief and Doubt. 16. Growth and Mental Structure. 17. Reasoning and the System of Beliefs. 18. Growth of Mental Structure.