The delicacy of brightness discrimination--Methods of testing the dancer's ability to detect slight differences in brightness--Results of tests with gray papers--Relation of intensity of visual stimuli to the threshold of discrimination--Weber's law apparatus and method of experimentation-- Results of Weber's law tests--Practice effects, the training of vision-- Description of the behavior of the dancer in the discrimination box experiments--Modes of choice: by affirmation; by negation; by comparison-- Evidence of indiscriminable visual conditions. CHAPTER IX THE SENSE OF SIGHT: COLOR VISION Does the dancer see colors?--The food-box method of testing color vision-- Waugh's food-box method--Results of tests--Tests by the use of colored papers in the visual discrimination box--Yellow-red vision--Blue-orange vision--Brightness vision _versus_ color vision--Brightness check tests--Green-blue vision--Violet-red vision--Conclusions. CHAPTER X THE SENSE OF SIGHT: COLOR VISION (_Continued_) The use of color filters--Testing color vision by the use of transmitted light--Green-blue vision--Green-red vision--Blue-red vision--Stimulating value of different portions of the spectrum--Does red appear darker to the dancer than to us?--Conclusions concerning color vision--Structure of the retina of the dancer and its significance. CHAPTER XI THE ROLE OF SIGHT IN THE DAILY LIFE OF THE DANCER. Sight and general behavior--Behavior of blinded dancers--Experimental tests of ability to perceive form--Visual guidance in mazes--Following labyrinth paths in the dark--The relative importance of visual, olfactory, and kinaesthetic stimuli--Conditions for the acquisition of a motor habit--Conditions for the execution of an habitual act. CHAPTER XII EDUCABILITY: METHODS OF LEARNING The modifiability of behavior--Educational value of experimental studies of modifiability--Methods: the problem method; the labyrinth method; the discrimination method--Relation of method to characteristics of animal-- Simple test of the docility of the dancer--Lack of imitative tendency-- Persistence of useless acts--Manner of profiting by experience--Individual differences in initiative. CHAPTER XIII HABIT FORMATION: THE LABYRINTH HABIT The labyrinth method--Problems--Preliminary tests--Comparison of the behavior of the dancer in a maze with that of the common mouse--Evolution of a labyrinth method--Records of time and records of errors--Simple and effective method of recording the path--Curves of habit formation--Regular and irregular labyrinths--Points for a standard labyrinth--Values and defects of the labyrinth method. CHAPTER XIV HABIT FORMATION: THE DISCRIMINATION METHOD