CONTENTS xi 



CHAP. PAGE 



XIV. THE MECHANISM OF HEREDITARY TRANSMISSION 206 



Weismann's theory The nucleus in heredity Ex- 

 periments of Boveri and of Herbst Chromosome 

 elimination in hybrids Oenothera Chromosome be- 

 haviour and Mendelian segregation Objections to the 

 hypothesis Gametic coupling (linkage) Drosophila 

 Crossing-over and chiasmatypy Sex -limited (sex- 

 linked) inheritance Non-disjunction Linkage in 

 male and female Chemical analogy Summary. 



XV. THE ROLE OF THE CYTOPLASM IN DEVELOPMENT 



AND HEREDITY ...... 241 



Hybridisation experiments Sperm nucleus in foreign 

 egg cytoplasm Degrees of incompatibility Cyto- 

 plasmic transmission Differential cell division 

 Organ-forming substances Centrifuge experiments 

 Equipotential systems Summary. 



XVI. CONCLUSION ....... 256 



Structure and function The problem of differentia- 

 tion Cytology and Physical Sciences Comparative 

 Cytology Origin of life Methods of investigation. 



BIBLIOGRAPHY ........ 266 



INDEX .......... 276 



