Contents 



IX 



and Their Relation to Cleavage 



Patterns 218 



Function of Partition Membranes 

 in Cellular Differentiation .... 220 



Factors Concerned in Shaping of 



the Blastula 221 



Gastrulation 223 



SECTION VI 

 EMBRYOGENESIS: PROGRESSIVE DIFFERENTIATION 



Chapter 1. Amphibians 



230 

 230 



BY J. HOLTFRETER AND V. HAMBURGER 



Egg Organization and Determina- 

 tion of Axes 230 



Gastrulation, Fate Maps 234 



Significance of Gastrulation Move- 

 ments and Induction as Organ- 

 izing Factors 235 



State of Organization of the Early 

 Gastrula 238 



Analysis of the "Organizer" .... 243 



The Organization of the Meso- 

 derm Mantle and the Tail Bud 

 in the Neurula 247 



Regional Induction Capacities of 

 the Mesoderm of the Neurula . 250 



Organization and Early Differen- 

 tiation of the Medullary Plate . 252 



The Induction of Neural Crest De- 

 rivatives and of other Ectoder- 

 mal Structures 254 



Competence 257 



Regional Host Influence 259 



Heteroplastic and Xenoplastic 

 Transplantations 263 



Analysis of the Physiological 

 Mechanism of Induction 265 



General Considerations 275 



Chapter 2. Teleosts and Birds . 



BY DOROTHEA RUDNICK 



The Pre-Cleavage Period 297 



The Cleavage Period 298 



\ Events during Gastrulation 300 



Primitive Organization of the Em- 

 bryo 306 



Concluding Remarks 311 



297 



Chapter 3. Selected Invertebrates 315 



BY RAY L. WATTERSON 



Visible Differences along the An- 

 imal-Vegetal Axis of Polarity . 315 



Extent of Specification of Cyto- 

 plasm Encountered in Un- 

 cleaved Eggs 316 



Are Extrinsic or Intrinsic Factors 

 Responsible for Establishment 

 of an Axis of Polarity? 317 



Stratification of Egg Constituents 

 along the Axis of Polarity Is the 

 Result, Not the Cause, of Polar 

 Organization 317 



Evidence that the Structural Basis 

 of Egg Organization Resides in 

 the Egg Cortex 318 



Specification of Blastomeres Ac- 

 cording to the Portion of the 

 Cytoplasm Segregated within 

 Them 318 



Interaction between Blastomeres 

 in Development 324 



Establishment of Dorsoventrality 

 and Bilaterality 331 



Chapter 4. Insects 337 



by DIETRICH BODENSTEIN 



The Initiation of Early Embryonic 



Organization 337 



Determination and Regulation . . 337 



Embryonic Induction between 



Germ Layers 338 



Cytoplasmic Determiners 339 



