Archive image from page 63 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 2 7' i5r 1. â iM Fig. 19. â Transverse section of the blastoderm of a pigeon's egg about 8| hours after fertihzation ( ). (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
Archive image from page 63 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 2 7' i5r 1. â iM Fig. 19. â Transverse section of the blastoderm of a pigeon's egg about 8| hours after fertihzation ( ). (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 P'iG. 20. â Transverse section of the l)lastoderm of a pigeon's egg at the end of the period of multiplication of sperm-nuclei, about 10 hours after fertil- ization ( ). (After Blount.) 1, Accessory cleavage around the sperm-nuclei. 2, Marginal cells; sharply separated from the sperm-nuclei. 3, Central cells. 4, Bperm-nuclei. as the hen's ovum of the same stage of development. In the hen's egg Patterson has shown that there is a very limited and incon- spicuous accessory cleavage (see Fig. 16 C) around the fewer supernumerary sperm-nuclei that occur. But most of these nuclei in the hen tend to pass into deeper portions of the disc and there undergo complete fragmentation without producing superficial furrows. Another feature brought out by these photographs requires emphasis. The periblast ring shows no definite outer margin,
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