Archive image from page 63 of The development of the chick;. The development of the chick; an introduction to embryology . developmentofchi00lill Year: 1908 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
Archive image from page 63 of The development of the chick;. The development of the chick; an introduction to embryology . developmentofchi00lill Year: 1908 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 Fig. 20. — Transverse section of the blastoderm of a pigeon's eg 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, Sperm-nuclei. as the hen's ovum of the same stage of development. It is doubt- ful whether the absence of accessory cleavage in the hen's egg should be taken as evidence that the fertilization is monospermic. It may well be that supernumerary sperm-nuclei are present without producing the appearance of accessory cleavage, owing, perhaps, to a deeper situation in the periblast. This point requires investigation. Another feature brought out by these photographs requires emphasis. The periblast ring shows no definite outer margin,
Size: 3042px × 658px
Photo credit: © Actep Burstov / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: 1900, 1908, archive, book, bookauthor, bookdecade, bookpublisher, bookyear, drawing, historical, history, illustration, image, lillie_frank_rattray_1870_1947, new_york_holt, page, picture, print, reference, vintage
