CONTENTS 



I. Introduction 4 



II . Methods of experiment and material 8 



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



blood 12 



1. Normal development up to the establishment of a circulation. ... 12 



2. History of experimental embryos to the time when circulation 



should begin 13 



3. Early formation of blood cells in living embryos 14 



a. Intra-embryonic blood cells 14 



b. Yolk-sac blood islands 14 



4. The five-day embryos 17 



5. The eight- and ten-day embryos ' 20 



6. Condition of the heart in old embryos without a circulation 28 



7. Development of the yolk-sac blood islands in life 29 



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

 cles as determined by study of microscopic sections 32 



1. The structure of the heart in embryos without a circulation 32 



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



as an intra-embryonic blood anlage 37 



3. Blood islands of the yolk-sac, their origin and development 42 



4. Fate of the blood corpuscles in embryos without a circulation. ... 48 



5. Has vascular endothelium haematopeotic power? 52 



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



corpuscles 54 



7. Environmental conditions necessary for blood cell multiplication 



and differentiation 60 



8. Question of haematopoetic organs? 62 



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 65 



1 . I ntroduction 65 



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



fish 66 



3. Vascular endothelium, and vascular growth and development. ... 76 



4. Haematopoesis, the monophyletic and polyphyletic views, etc 83 



VI. Summary and conclusions 92 



Literature cited. . . 99 



