. The development of the chick; an introduction to embryology. Birds -- Embryology. 46 THE DEVELOPMENT OF THE CHICK the accessory cleavage-cells and also in the unsegmented periblast (Figs. 19 and 20), they decrease in number as the accessory cleavage planes disappear, and when the latter are entirely lost. 1 •> Fig. 19. — Transverse section of the blastoderm of a pigeon's egg about 8| hours after fertilization ( ). (After Blount.) 1, Accessory cleavage. 2, Migrating sperm-nuclei, a, b, c, d, Cells of primary cleavage. the periblast is absolutely devoid of nuclei. Fragmentation of t
. The development of the chick; an introduction to embryology. Birds -- Embryology. 46 THE DEVELOPMENT OF THE CHICK the accessory cleavage-cells and also in the unsegmented periblast (Figs. 19 and 20), they decrease in number as the accessory cleavage planes disappear, and when the latter are entirely lost. 1 •> Fig. 19. — Transverse section of the blastoderm of a pigeon's egg about 8| hours after fertilization ( ). (After Blount.) 1, Accessory cleavage. 2, Migrating sperm-nuclei, a, b, c, d, Cells of primary cleavage. the periblast is absolutely devoid of nuclei. Fragmentation of the sperm-nuclei is a frequent accompaniment of their disappearance. Thus the accessory cleavage is a secondary and transient feature of the cleavage of the pigeon's egg due to polyspermy. After it has passed, the ovum is in precisely the same condition. 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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