TABLE OF CONTENTS 



C. Are^ Centrales and Foveje 181 



The Area Centralis, 181 — The Fovea, 182 — Distribution, 

 184. 



D. Intra-Ocular Color-Filters 191 



Types and Distribution, 191 — The Color- Vision Theory, 



192 — Yellow Filters and Chromatic Aberration, 193 — 

 Other Values, 195— Red Filters and the Rayleigh Effect, 

 197— Value of Red Oil-Droplets in Birds, 197— Value of 

 Red Oil-Droplets in Turtles, 197 — Phylogeny and Chem- 

 istry of the Intra-Ocular Filters, 199. 



9. ADAPTATIONS TO NOCTURNAL ACTIVITY . . 206 



A. Nocturnality and the Eye 206 



Noctumality and Crude Vision, 206 — Advantages and 

 Limitations, 208 — Lightless Habitats and their Conquest, 



209— Tne Eye as a Whole, 210— Tubular' Eyes, 212— 

 Spherical Lenses, 213 — Broad Comeae, 214. 



B. The Nocturnal Retina 215 



Rod: Cone Ratios, 215 — Pure- Rod Animals, 216 — Sum- 

 mation, 216. 



C. The Slit Pupil 217 



Value of the Slit Form, 218 — -Distribution and Meanings 

 of Pupil Shapes, 219. 



D. The Tapetum Lucidum 228 



Value and Basis of Eyeshine, 229 — The Tapetum Fibro- 



sum, 231 — The Tapetum Cellulosum, 233 — Guanin and 

 the Argentea, 235 — Guanin in Retinal Tapeta, 236 — Other 

 Retinal Tapeta, 238 — Guanin in Chorioidal Tapeta, 238 — 

 Phylogeny and Relative Efficiency of Tapeta, 243— The 

 Tapetum and Visual Acuity, 245. 



10. ADAPTATIONS TO SPACE AND MOTION . . .247 

 A. Accommodation and its Substitutes .... 247 

 Dependence of Apparent Distance upon Size, 247 — The 

 Why of Accommodation, 249— Devices Which Make 

 Accommodation Unnecessary, 253 — Vertebrate Methods 

 of Accommodation, 257 — Lampreys, 258 — Elasmobranchs, 

 260— Teleosts, 260--Other Fishes, 263— Matthiessen's 

 Ratio, 2&\ — Optical Elimination of the Cornea, 2M — Con- 

 sequences of Lens Movement, 265 — Amphibians, 265 — 

 Role of the Vitreous in Ichthyopsidan Accommodation, 268 

 — Sauropsidan Muscles of Accommodation, 269 — Scleral 

 Ossicles in Sauropsida, 270 — Accommodation in Saurop- 

 sida (Except Snakes), 275 — Special Features in Birds and 

 Lizards, 279— Snakes, 282— Mammals, 283. 



