CONTENTS 



CHAPTER I 



PAGK 



INTRODUCTORY 1 



CHAPTER II 



CELL-DIVISION AND GROWTH. 



1. Cell-division 22 



2. Growth 58 



CHAPTER III 



EXTERNAL FACTORS. 



1. Gravitation ........ 78 



2. Mechanical agitation ....... 89 



3. Electricity and magnetism . . . . . .91 



4. Light 93 



5. Heat 97 



6. Atmospheric pressure. The respiration of the embryo . 109 



7. Osmotic pressure. The role of water in growth . .115 



8. The chemical composition of the medium . . .126 



9. Summary . . . . . . . . .155 



CHAPTER IV 



INTERNAL FACTORS. 



(-1) The initial structure of the germ as a cause of differen- 

 tiation. 



1. The modern form of the preformationist doctrine . .158 



2. Amphibia 163 



3. Pisces ' 178 



4. Ampliioxus . . . . . . . .179 



