CONTENTS xiii 



CHAPTER XV 



PAGE 



MENDELISM AND MUTATION 336 



Mendelism A typical case of Mendelian inheritance The cytological 

 basis of Mendelism Mutation Mutations accompanied by changes 

 in chromosome number Bearing on the origin of species and varieties 

 Mutations accompanied by no change in chromosome number Conclusion. 



CHAPTER XVI 



SEX 354 



Experimental evidence for sex-determination Sex-chromosomes Sex- 

 chromosomes and Mendelism Experimental alteration of the sex ratio 

 Metabolic theories of sex General discussion. 



CHAPTER XVII 



LINKAGE -. . 378 



A typical case of linkage Sex-linkage Non-disjunction Linkage groups 

 The chiasmatype theory Application of the chiasmatype theory to the 

 problem of linkage General discussion Other theories of linkage Value 

 of chromosome theory of heredity. 



CHAPTER XVIII 



WEISMANNISM AND OTHER THEORIES 398 



Darwin's hypothesis of pangenesis DeVries's theory of intracellular 

 pangenesis Nageli's idioplasm theory Weismann's theory Some modern 

 aspects of Weismannism Non-factorial theories A chemical theory of 

 heredity Conclusion Bibliography 14 (for Chapters XIV-XVIII). 



INDEX. . 427 



