CONTENTS xi 



11 -THE NERVOUS SYSTEM 159 



Neural crests and their derivatives, 159 

 Transformation of neural tube into spinal cord, 1 62 

 The brain and its derivatives, 1 64 

 Sensory elements of the nose, ear, and eye, 167 



12 • THE CIRCULATORY SYSTEM 171 



The extraembryonic membranes, 172 



Formation of blood vessels and the heart, 1 75 



The aortic arches, 1 79 



Development and regression of the renal portal circulation, 1 80 



Hepatic portal system, 1 80 



Changes in circulation with hatching, 1 82 



13 • THE DIGESTIVE TRACT 185 



Differentiation in the foregut region, 1 87 

 Derivatives of the midgut, 189 

 The hindgut, 1 90 



14 • THE SOMITES, NEPHROTOME, AND LATERAL MESODERM 193 



Development of the somites, 1 93 

 Differentiation of the nephrotome, 194 

 The lateral mesoderm, 200 



15 • THE DEVELOPMENT OF THE CHICK EMBRYO 203 



Cleavage, 204 



Gastrulation, 206 



Development during the first day of incubation, 208 



Development during the second day, 21 1 



The 48-hour embryo, 215 



The 72-hour chick embryo, 222 



Subsequent development, 227 



16 • REGENERATION 229 



Dynamic state in the adult, 229 



Regeneration in various species, 231 



Polarity in regeneration, 231 



Theories of regeneration, 234 



Origin of the cells for regeneration, 236 



Nature of dedifferentiation, 238 



Role of nerves, 239 



Stimulus for regeneration, 239 



17 • GROWTH AND REDUPLICATION 243 



Growth in relation to time, 244 

 Growth in microorganisms, 244 



