TABLE OF CONTENTS. 1. The shell. 2. The shell-membrane. 3. The albumen. 4. The vitelling membrane. 5. The yolk. 6. The yellow yolk. 7. The white yolk. 8. The white yolk-spheres. 9. The structure of the blastoderm. 10. Recapitulation, II. The ovarian ovun. 12. The descent of the ovum along the oviduct, 13. The impregnation of the ovum. 14. Segmentation. 15. The formation of the upper and lower layers. A BRIEF SUMMARY OF THE WHOLE HISTORY OF INCUBATIO8, pp. 27 -42, 1. The embryo is formed in the area pellucida. 2. The epiblast, moblunt, and hypoblast. 3. The extension of the blastoderm over the yolk. 4. Th THE CHANGES WHICH TAKE PLACE DURING THE FIRST DAY OF INCUBATION, 1. Variations in the progress of development. 2. The embryonic shield. THE CHANGES WHICH TAKE PLACE DURING THE SECOND DAY, pp. 58-83. 1. Increasing distinctness and prominence of the embryo. 2. The first cere- bral vesicle. 3. The increase in the number of protovertebræ. 4. The first THE CHANGES WHICH TAKE PLACE DURING THE THIRD DAY, pp. 84-140. 1. The diminution of the albumen. 2. The spreading of the opaque and vascular areas. 3. The vascular area. 4. The continued folding in of the embryo. 5. The increase of the amnion. 6. The change in the position of the embryo. 7. The curvature of the body. 8. The cranial flexure. 9. Growth of the vesicles of the cerebral hemispheres; the third ventricle, pineal gland, infundibulum and pituitary body, the cerebellum and medulla oblongata. 10. Changes in the spinal cord. II. The formation of the eye. Histological changes in the retina, optic nerve, and lens. 12. The formation of the ear. aortic arches. 16. Changes in the heart; the Ductus Cuvieri and cardinal veins. 17. The folding in of the alimentary canal; the formation of the tail. 18. The lungs. 19. The liver. 20. The pancreas and spleen. 21. The thyroid body. 22. Changes in the trunk of the embryo. 23. Separation of the muscle-plates from the proto vertebræ. 24. Growth of the intermediate cell-mass. 25. The cranial nerves. 26. The Wolffian duct. 27. Recapi- CHAPTER VI. I. Appearances on opening the egg. 2. Growth of the amnion. 3. Narrowing of the splanchnic stalk. 4. Increase in the cranial flexure. 5. The first appearance of the limbs. 6. Growth of the head. 7. Changes in the nasal pits. 8. Formation of the mouth. 9. The cranial nerves. The allantois. 11. Changes in the protovertebræ; the spinal ganglia. 12. The secondary segmentation of the vertebral column. 13. Changes in the notochord. 14. Ossification of the vertebræ. Changes in the muscle-plates. 17. The Wolffian body and duct. 18. duct of Müller. 19. The kidneys. Changes in the arterial system. 22. Changes in the venous system; the veins of the liver. 23. Changes in the heart; the ventricular septum. 1. Appearances on opening the egg. 2. The growth of the limbs. 3. The cranium; the investing mass and trabecula. 4. Changes in the I. The commencement of distinct avian differentiation. 2. The fœtal appendages during the sixth and seventh days. 3. During the eighth, ninth and tenth days. 4. From the eleventh to the sixteenth day. 5. From the sixteenth day onwards. 6. The changes in the general form of the embryo during the sixth and seventh days. 7. During the eighth, ninth and tenth days. 8. From the eleventh day onwards; feathers, ossifications. 9. Changes in the venous system before and after the commencement of pulmonary respi- ration. 10. Changes in the arterial system, the modifications of the aorti arches. 11. Summary of the chief phases of the circulation. 12. I, 2. The primordial cranium. 3, 4. The investing mass of Rathke. IO. The maxillary process. 8. The mandibular arch. 9. The hyoid arch. 15. Formation I. Incubators. II. Examination of a 36 to 48 hours embryo. Examination of an embryo of about 48-50 hours. IV. Of an embryo at the end of the third day. V. Of an embryo of the fourth day. VI. Of a blastoderm of 20 hours. VII. Of an unincubated blastoderm. VIII. Of the process of segmentation. IX. Of the later changes of the embryo. X. Study ERRATUM. p. 124, in the description of Fig. 39 B, for 'Superior vertebral' substitute 2. DIAGRAMMATIC Section of an Unincubated Fowl's Egg A. Yellow yolk-sphere filled with fine granules. B. White yolk- 3. Section of a Blastoderm of a Fowl's Egg at the commencement of 15 18 4. Section through the Germinal Disc of the ripe Ovarian Ovum of a 19 5. Surface Views of the early Stages of the Segmentation in a Fowl's Egg 22 6. Surface View of the Germinal Disc of a Hen's Egg during the later Stages of Segmentation 7. Section of the Germinal Disc of a Fowl during the later Stages of Segmentation 8. A to N. A series of purely diagrammatic representations introduced to facilitate the comprehension of the manner in which the body of the embryo is formed, and of the various relations of the yolk-sac, amnion and allantois 23 24 29-32 9. Diagrammatic Longitudinal Section through the Axis of an Embryo. 33 IO. Section of a Blastoderm at right angles to the long axis of the |