X TABLE OF CONTENTS 



IX. Triploids 131 



X. Haploids 139 



XL 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 Number 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 



Sex in Haploids 239 



Sex and its Definition in Lower Plants 242 



XVL Intersexes 251 



Intersexes from Triploid Drosophila 251 



Intersexes in the Gypsy Moth 254 



The Free Martin " 258 



XVIL Sev Reversals 261 



Environmental Changes 262 



