TABLE OF CONTENTS xiii 



PAGE 



CHAPTER XXVI. HEREDITY IN PURE LINES. H. H. N. . . . . 376 



Are Determiners (Genes) Constant or Variable ? 378 



CHAPTER XXVII. MENDEL'S LAWS OF HEREDITY 380 



Mendel's Life and Character. J. Arthur Thomson 380 



Mendel's Discoveries. /. Arthur Thomson 380 



Mendel's Explanations. /. M. Coulter and M. C. Coulter . . . 386 

 Illustrations of Simple Mendelian Inheritance in Both Animals and 



Plants. /. Arthur Thomson 393 



CHAPTER XXVIII. THE PHYSICAL BASIS OF MENDELISM. Ernest 



B. Babcock and Roy E. Clausen 401 



CHAPTER XXIX. NEO-MENDELISM IN PLANTS. John M. Coulter 



and Merle C. Coulter 413 



Presence and Absence Hypothesis 413 



Blends 415 



The Factor Hypothesis 417 



CHAPTER XXX. NEO-MENDELIAN HEREDITY IN ANIMALS. H. H. N. 429 



Illustrations of the Factor Hypothesis 429 



The Factorial Analysis of Color in Mice 429 



Different Kinds of Albinos 430 



Castle's Guinea Pigs 431 



CHAPTER XXXI. SEX-LINKED AND OTHER KINDS OF LINKED 

 INHERITANCE IN Drosophila AND OTHER SPECIES. William E. 



Castle 433 



Drosophila Type and Poultry Type of Sex-linked Inheritance . . 436 



CHAPTER XXXII. LINKAGE AND CROSSING-OVER. William E. 



Castle 441 



CHAPTER XXXIII. SEX DETERMINATION. H.H.N 449 



Various Theories of Sex Determination 449 



The Chromosomal Mechanism of Sex Determination .... 450 



Sex Determination in Parthenogenetic Species 451 



The Poultry Type of Sex Determination 452 



Sex Differentiation 453 



PART V. EUGENICS 



CHAPTER XXXIV. THE INHERITANCE OF HUMAN CHARACTERS, 



PHYSICAL AND MENTAL. Elliot R. Downing 459 



CHAPTER XXXV. HUMAN CONSERVATION. Herbert E. Walter . . 473 



How Mankind May Be Improved 473 



More Facts Needed 473 



Further Application of What We Know Necessary 474 



The Restriction of Undesirable Germplasm 475 



Control of Immigration 475 



