THE ORIGIN OF BLOOD AND VASCULAR ENDOTHE- 

 LIUM IN EMBRYOS WITHOUT A CIRCULATION 

 OF THE BLOOD AND IN THE NORMAL EMBRYO 



CHARLES R. STOCKARD 



Department of Anatomy, Cornell University Medical School, New York City 



FORTY-NINE FIGURES 



CONTENTS 



I. Introduction 228 



II. Methods of experiment and material 232 



III. The study of living embryos with and without the circulation of the 



blood ' 236 



1. Normal development up to the establishment of a circulation. . . . 236 



2. History of experimental embryos to the time when circulation 



should begin 237 



3. Early formation of blood cells in living embryos 238 



a. Intra-embryonic blood cells 238 



b. Yolk-sac blood islands 238 



4. The five-day embryos 241 



5. The eight- and ten-day embryos 244 



6. Condition of the heart in old embryos without a circulation 252 



7. Development of the yolk-sac blood islands in life 253 



IV. The origin and histogenesis of vascular endothelium and blood corpus- 

 cles as determined by study of microscopic sections 256 



1. The structure of the heart in embryos without a circulation 256 



2. The intermediate cell mass; its origin, position and significance 



as an intra-embryonic blood anlage 261 



3. Blood islands of the yolk-sac, their origin and development 266 



4. Fate of ihe blood corpuscles in embryos without a circulation. . . . 272 



5. Has vascular endothelium haematopeotic power? 276 



6. The origin of lymphocytes and leucocytes or so-called white blood 



corpuscles 278 



7. Environmental conditions necessary for blood cell multiplication 



and differentiation 284 



8. Question of haematopoetic organs? 286 



V. A consideration of the experimental study on the origin of blood in 



Teleosts in relation to the more recent studies on the origin and 

 development of vessels and blood cells 289 



1 . Introduction 289 



2. The specific problems of blood and vessel formation in the bony 



fish 290 



3. Vascular endothelium, and vascular growth and development. . . . 300 



4. Haematopoesis, the monophyletic and polyphyletic views, etc 307 



VI. Summary and conclusions 316 



Literature cited 323 



227 

 t 



THE AMERICAN JOURNAL OF AN.\TOMy, VOL. 18, NO. 2 



