TABLE OF CONTENTS IX 



tion, 141; Discontinuous and continuous variation, 141; Congeni- 

 tal and acquired variation, 142; Determinate variation, 150; The 

 causes of variation, 154, 156; Variation as related to amphimixis 

 and parthenogenesis as mutations of de Vries, 154. 



^CHAPTER X. HEREDITY. 



Hereditary variancy defined, 163; Atavism or reversion, 166; 

 Telogony, 166; Prenatal influences, 167; Not all transmission is 

 heredity, 168; Determination of sex, 170; Homologies and analo- 

 gies, 172; Vestigial organs, 174; Significance of vestigial organs, 

 181; Heredity and its "laws," 181; Galton's law of ancestral in- 

 heritance, 184; Mendel's law of alternative inheritance, 187; 

 Modification of Mendelism, 188. 



M^ CHAPTER XI. INHERITANCE OF ACQUIRED CHARACTERS. 



The Lamarckian principles of evolution, 196; Neo-Lamarckism 

 and Neo-Darwinism, 197; Acquired characters, 198; Effects of use 

 and disuse, 199; Environmental modifications not inherited, 200; 

 Examples of non-inheritance of acquired characters, 201 ; Heredity 

 unproved, 203; Convergence of characters and parallelism, 204; 

 Actual effects of environment, 205 ; Ontogenetic species, 206. 



CHAPTER XII. GENERATION, SEX, AND ONTOGENY. 



Generation and ontogeny, 211 ; Spontaneous generation or abio- 

 genesis, 212; Simplest modes of generation, 213; Parthenogenesis, 

 215; Differentiation of reproductive cells, 217; Simplest many- 

 celled animals, 218; Effects of sex, 220; Sex dimorphism, 221; 

 The life cycle, 223; The egg, 224; Numbers of young, 225; Em- 

 bryonic and post-embryonic development, 227; Developmental 

 stages, 229; Continuity of development, 231; Metamorphosis or 

 apparent discontinuity, 234; Significance of facts -of develop- 

 ment, 234; Divergence of development, 234; The duration of 

 life, 240; Death, 241. 



CHAPTER XIII. FACTORS IN ONTOGENY, AND EXPERIMENTAL 

 DEVELOPMENT. 



Processes in ontogeny, 244 ; Extrinsic and intrinsic factors, 245 ; 

 Mechanism versus vitalism, 246; Functions of protoplasm, 247; 

 Ultimate structure of protoplasm, 248; Theories of organic units, 

 250; Cell division, 251 ; Mitosis, or karyokinesis, 252; Somatic and 

 germ tissues, 257; Reproduction in protozoa, 260; Maturation, 

 264; Fertilization, 267; Cleavage, 269; Reduction of the chromo- 

 somes, 269; Preformation versus epigenesis, 276; Examples giving 



