CONTENTS. ix 



SECTION VI. 

 THE STRUCTURE OF THE RETINA. 



I'AGK 



737. The Optic Nerve 55 



738. The Layers of the Retina ' . . . 56 



739. The Neuroglial Elements 57 



740. The Nervous Elements. The Rods arid Cones with the Rod Fibres 



and Cone Fibres '. 59 



$ 741. The Inner Nuclear Layer 62 



742. The Layer of Ganglionic Cells and Layer of Optic Fibres ... 64 



743. The Probable Connection of the Several Elements 64 



744. The Macula Lutea and Fovea Centralis 66 



745. The Blood-vessels of the Retina 67 



746. The Pigment Epithelium 68 



SECTION VII. 

 ON SOME GENERAL FEATURES OF VISUAL SENSATIONS. 



747. The Relation of the Sensation to the Intensity of the Stimulus; 



Weber's Law 71 



748. The Relation of the Sensation to the Duration of the Stimulus . . 74 



749. Flickering and Continuous Sensations . 75 



750. Sensations produced by various Changes in the Retina referred to 



some External Source of Light, 76 



751. Localisation of Visual Sensations 77 



752. The Conditions of Discrete Visual Sensations 79 



753. The Region of Distinct Vision. The Limits of Distinct Vision . 80 

 754. Nature of the Discreteness of Visual Sensations ; Retinal Visual 



Units 81 



SECTION VIII. 

 ON COLOUR SENSATIONS. 



755. The Existence of many Kinds of Colour Sensations 84 



756. The Mixing of Colour Sensations 85 



757. The several usual Colour Sensations result from the Mixture of 



Simpler, Primary Sensations 86 



758. The Conditions which determine the Characters of Colour Sensations 88 



759. Complementary Colours 89 



760. Any Colour Sensation produced -by the suitable Mixture of Three 



Colour Sensations 90 



761. The Young-Helmholtz Theory of Colour Sensations 91 



762. Bering's Theory of Colour Sensations. A Comparison of the Two 



Theories 93 



