X PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



SECTION III. 



The Retina and its Functions. 



Structure of the retina, 117. Its layers, 118. Bacillary layer, dis- 

 tribution of the rods and cones, 119. Distinctive function of the lay- 

 ers, 120 ; of the rods and cones, 121. Visual purple, 121. 



SECTION IV. 

 Perception of Space and of Objects in Space. 



First Law of Vision. Law of Spatial Reference of Retinal Impres- 

 sions, 122. — Comparison with other senses, 123. Illustrations of the 

 law : (1) Irritation of retina, (2) phosphenes, (3) muscse volitantes, 124. 

 (4) Purkinje's figures, (5) ocular spectra, 125 ; generalization, 126. 



Second Law of Vision; Law of Direction, 126. — Comparison with 

 other senses, 128. Explanation of some visual phenomena : (1) erect 

 vision, explanation, 129. (2) Fovea and its spatial representative, 130 ; 

 minimum visibile, 131 ; compare with touch, 132. (3) Elind spot, 

 132 ; experimental proof, 133 ; spatial representative of, 134. 



Color Perception and Color-blindness, 135. — Intensity vs. color, 

 primary colors, 136. Theory of color perception, general theory, 137. 

 Special theories, 138. Color-blindness, 139. Cause of coloi-blind- 

 ness, what the color-blind see, 140. Tests of color-blindness, 141. 



SECTION V. 

 Binocular Vision. 



Definition, 142. Single and double vision, 142. Experiments illus- 

 trating double vision, single vision, 143. Corresponding points, 144. 



Third Law of Vision ; Law of Corresponding Points. — Conditions 

 of single vision illustrated, 144. Horopteric circle and horopter defined, 

 146. Relation of chiasm to corresponding points, 147. The two ad- 

 justments of the eyes, two kinds of corresponding points, 148. Two 

 fundamental laws of vision, 149. 



Binocular perspective, experiments illustrating, 149. Limitation of 

 clear vision, 151. Different forms of perspective : (1) Aerial, 151 ; (2) 

 mathematical, (3) binocular, (4) focal, 152. 



Judgments of She and Distance. — Distance, size, 153. Form, gra- 

 dations of judgments, 155. 



SECTION VI. 



Comparative Physiology and Morphology of the Eye. 



Vertebrates. 



Mammals : Iris, pupil, tapetum, 156 ; fovea, 157. Birds : iris, 

 sclerotic bones, nictitating membrane, 157 ; fovea, 158. Reptiles, 158! 

 Fishes, binocular vision in vertebrates, 159. Chiasm in vertebrates! 

 position of the eyes, 160. Fovea, 161. 



