. The development of the chick; an introduction to embryology. Birds -- Embryology. DEVELOPMENT PRIOR TO LAYIXG 45 The question arises whether the disappearance of the cell- walls around the sperm-nuclei is caused by degeneration of the latter, or is simply a later syncytial condition in the periblast in B. C D Fig. 18. — Photographs of the cleavage of the pigeon's ovum (after Mary Blount). The figures are so arranged that the axis of the shell is across the page with the large end to the left. The future axis of the embryo is therefore inclined 45° to the margin of the page with the anterior
. The development of the chick; an introduction to embryology. Birds -- Embryology. DEVELOPMENT PRIOR TO LAYIXG 45 The question arises whether the disappearance of the cell- walls around the sperm-nuclei is caused by degeneration of the latter, or is simply a later syncytial condition in the periblast in B. C D Fig. 18. — Photographs of the cleavage of the pigeon's ovum (after Mary Blount). The figures are so arranged that the axis of the shell is across the page with the large end to the left. The future axis of the embryo is therefore inclined 45° to the margin of the page with the anterior end to the right above. A. A very regular sixteen-celled stage; accessory cleavage well shown; though not well focused on the lower margin. B. Approximate thirtv-two celled stage. There is no accessory cleavage in this case. The formation of the central from the margmal cells may be readily observed in this figure. C. Later stage of cleavage. , D. Cleavaiie at The marjrinal cells are now becommg separated peripherally from the periblast which has received its nuclei from them. which the sperm-nuclei are embedded. There can be little doubt that the former alternative is correct. While in the stages of the accessory cleavage, sperm-nuclei are readily found both m. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lillie, Frank Rattray, 1870-1947. New York, Holt
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