12 Contents 



CHAPTER 14 Page 



THE REPRODUCTIVE SYSTEM 252 



Functions of the Reproductive System, 254 ; The Male Reproductive 

 System, 255 ; The Testes, 255 ; The Ducts of the Reproductive System, 

 257 ; The Penis, 258 ; The Glands of the Reproductive System, 258 ; The 

 Sperm, 258 ; The Female Reproductive System, 259 ; The Ovaries, 260 ; 

 The Reproductive Tract, 260 ; The Egg, 262 ; The Mammary Glands, 262 ; 

 Menstruation, 262 ; Pregnancy, 263 ; Estrus, 263. 



SECTION III 

 THE CELL AS THE BASIS OF ORGANIC ACTIVITY 



CHAPTER 15 



CELLS AND THEIR ACTIVITIES 265 



The Structure of the Cell, 267; The Nucleus, 267; The Cytoplasm, 268; 

 Cell Division, 270 ; Mitosis, 270 ; Amitosis, 272 ; Chromosome Number, 272 ; 

 Meiosis, 273 ; Spermatogenesis, 273 ; Oogenesis, 275 ; Fertilization, 276. 



CHAPTER 16 



EMBRYOLOGY 278 



Early Embryology, 280 ; Cleavage, 280 ; Blastula Formation, 280 ; Gastru- 

 lation, 282 ; Mesoderm Formation, 282 ; The Effect of Yolk, 282 ; Primitive 

 Streak, 284; Early Human Embryology, 284; Organogeny, 287; Ecto- 

 derm, 287 ; Entoderm, 288 ; Mesoderm, 288 ; The Embryonic Germ Layers 

 and Their Derivatives, 289 ; Embryonic Membranes, 290 ; Yolk Sac, 290 ; 

 The Amnion and Chorion, 290 ; The Allantois, 291 ; The Placenta, 292 ; 

 Parturition, 292 ; Experimental Embryology, 293 ; Organization of the Egg, 

 293 ; Transjplants of Embryonic Tissues, 294 ; Embryonic Determiners or 

 Organizers, 294 ; Twins and Twinning, 295. 



CHAPTER 17 



GENETICS 296 



The First Mendelian Law, 298 ; The Study of a Single Character, 298 ; A 

 Monohybrid Cross, 298 ; Monohybrid Crosses Without Dominance, 300 ; 

 The Physical Explanation of Segregation, 301 ; Drosophila as an Experi- 

 mental Animal, 302 ; The Second Mendelian Law, 303 ; The Study of Two 

 Characters, 303 ; A Dihybrid Cross, 303 ; Multihybrid Crosses, 304 ; In- 

 teraction of Factors, 304; Multiple Alleles, 307; Sex Linkage, 307; The 

 Chromosomal Mechanism, 308 ; Sex-Linked Characters, 309 ; Sex-Limited 

 Characters, 310; WZ Sex Determination. 310; Mutations, 311; Gene 

 Mutations, 311; Lethal Characters, 312; Linkage, 312; A Cross Involv- 

 ing Linked Genes, 313; Crossing Over, 313; Chromosomal Maps, 314; 

 Cytoplasmic Inheritance, 315; Biochemical Genetics, 316; The Application 

 of Genetic Principles, 316; Inbreeding, 317; Outbreeding, 317; Human 

 Genetics, 317. 



CHAPTER 18 



EVOLUTION _ 319 



The Origins of Life, 320 ; Development of the Idea, 321 ; The Evidences 

 of Evolution, 323 ; Comparative Anatomy, 323 ; Comparative Embryology, 

 324; Vestigial Organs, 324; Comparative Physiology, 324; Paleontology. 

 325 ; Classification, 325 ; How Evolution Occurs. 325 ; The Inheritance of 

 Acquired Characters, 326; Darwin's Theory, 327; Neo-Darwinism, 328; 

 Criticisms of Neo-Darwinism, 329: Orthogenesis and the History of the 

 Horse, 330; The Evolution of the Horse, 331 ; Eohippus, 331 ; Mesohippus, 



