viii TABLE OF CONTENTS 



IX. Triploids 131 



X. Haploids 139 



XI. Polyploid Series 150 



The Polyploid Wheats 150 



The Polyploid Roses 158 



Other Polyploid Series 165 



XII. Heteroploids 172 



XIII. Species Crossing and Changes in Chromo- 



some Nnmber 191 



XIV. Sex and Genes 199 



The Insect Type (XX-XY) 199 



The Avian Type (WZ-ZZ) 206 



Sex-Chromosomes in Dioecious Flowering Plants 212 



Sex-Determination in Mosses 214 



XV. Other Methods of Sex-Determination Involv- 



ing the Sex-Chromosomes 219 



The Attachment of the X-Chromosome to Auto- 

 somes 219 

 The Y-Chromosome 222 

 Degeneration of Male-Producing Sperm 228 

 The Elimination of one X-Chromosome from a Dip- 

 loid Egg to Produce a Male 228 

 Sex-Determination through the Accidental Loss of 



a Chromosome in Spermatogenesis 231 



Diploid Females and Haploid Males 233 



XVI. Intersexes 240 



Intersexes from Triploid Drosophila 240 



Intersexes in the Gypsy Moth 243 



The Free Martin 247 



XVII. Sex Reversals 250 



Environmental Changes 251 



Changes of Sex Associated with Age 254 



