CONTENTS Xi 



CHAPTER PAGE 



XIV. COORDINATION IN ANIMALS Continued 



C. Sense Organs 193 



1. Cutaneous Senses 195 



2. Sense of Taste 195 



3. Sense of Smell 196 



4. The Ear 196 



5. The Eye 198 



XV. REPRODUCTION IN ANIMALS 203 



XVI. ORIGIN OF THE INDIVIDUAL 209 



A. Origin of Life 209 



B. Reproduction 212 



C. Origin of the Germ Cells 223 



1. Mitosis 224 



2. Gametes 228 



3. Spermatogenesis 230 



4. Oogenesis - 232 



5. The Chromosome Cycle 233 



6. Fertilization 237 



D. Significance of Fertilization 242 



1. Protista 243 



2. Metazoa 249 



E. Organization of the Zygote 251 



XVII. HERITAGE OF THE INDIVIDUAL 261 



A. Heritability of Variations 264 



1. Modifications 265 



2. Combinations 268 



3. Mutations . . . .... . . .269 



B. Galton's 'Laws' 269 



C. Mendelism 271 



1. Monohybrids . . . . ." . . . . 272 



2. Dihybrids . , . . 276 



3. Trihybrids ........ 280 



4. General Principles . . ; . . . . . : 280 



D. Neo-Mendelism 282 



E. Mechanism of Mendelian Inheritance .... 287 



1. Sex Determination . . . . . . . 291 



2. Linkage ...... 293 



F. Nature versus Nurture . . . 296 



G. Selection . . .... '. 299 



Pure Lines 303 



Summary 306 



