TABLE OF CONTEXTS xi 



Cliano;es of Sex Associated with Ag^e 265 



Sex and Sex Reversal in Frogs 267 

 Transformation of Bidder's Organ of the Male Toad 



into an Ovary 277 



Sex Reversal in Miastor 280 



Sex Reversal in Birds 282 



The Effect of Ovariotomy in Birds 283 



The Sex of Parabiotic Salamander Twins 286 



Sex Reversal in Hemp 287 



XVIII. Stability of the Gene 292 



XIX. General Conclusions 311 



The Effects Produced by a Change in Chromosome 



Number and bv a Change in a Gene 311 



Is the Mutation Process Due to a Degradation of the 



Gene ? 318 



Are Genes of the Order of Organic Molecules ? 320 



Bibliography 322 



Index 352 



