CHAPTER IV 



THE EARLY DEVELOPMENT OF THE CHICK 

 THE EMBRYONIC MEMBRANES AND APPENDAGES 



PAGE 

 INTRODUCTION. . . 229 



I. THE EGG AND ITS PRODUCTION 232 



1. The Egg 232 



2. The Reproductive Organs of the Fowl 234 



3. The Formation of the Egg and its Early Development . . . 236 



A. The History of the Ovarian Ovum to Ovulation . . 236 



B. The Period from Ovulation through Fertilization . . 240 



C. From the Beginning of Cleavage to the Time of Laying 241 



D. Gastrulation . . 248 



II. THE FORMATION OF THE EMBRYO 251 



III. THE EARLY DEVELOPMENT OF THE EMBRYO .... 260 



1. The Head-fold . . . 260 



2. Mesoderm 262 



3. Endoderm 267 



4. The Nervous System 269 



5. The Vascular System 271 



IV. THE EMBRYO OF ABOUT THIRTY HOURS (10-12 PAIRS 



OF SOMITES) 275 



V. THE SEPARATION OF THE EMBRYO FROM THE EXTRA- 



EMBRYONIC STRUCTURES 279 



VI. THE ESTABLISHMENT OF THE EXTERNAL FORM OF THE 

 EMBRYO 282 



VII. THE EMBRYONIC MEMBRANES AND APPENDAGES . . 286 



1. The Yolk-sac 286 



2. The Amnion 292 



3. The Allantois 295 



MANY of the great embryological classics are based upon the 

 development of the chick. The pioneer works of Harvey, of 

 Malpighi, of Wolff, Pander, and Von Baer, bear witness to the 

 fact that answers to many of the fundamental problems of the 

 science of embryology were sought in the development of Ihis 



229 



