. Text-book of embryology. Embryology. SEGMENTATION 13 in an egg in which the proportion of approaches the maximum. In this case the zygote nucleus commonly undergoes two mitotic divisions before there is any external symptom of segmentation of the cytoplasm. Usually a single furrow makes its appearance first, incising the surface of the germinal disc but not extending to its periphery (Fig. 8, A). Occasionally a second regular furrow makes its appearance intersecting the first at right angles. Fig. 7.—Vertical (meridional) sections through blastulae of Frog. (From Morgan, 1897.)
. Text-book of embryology. Embryology. SEGMENTATION 13 in an egg in which the proportion of approaches the maximum. In this case the zygote nucleus commonly undergoes two mitotic divisions before there is any external symptom of segmentation of the cytoplasm. Usually a single furrow makes its appearance first, incising the surface of the germinal disc but not extending to its periphery (Fig. 8, A). Occasionally a second regular furrow makes its appearance intersecting the first at right angles. Fig. 7.—Vertical (meridional) sections through blastulae of Frog. (From Morgan, 1897.) AR, commencing invagination ; SG, segmentation cavity. and it is a curious point that it is sometimes this second furrow which corresponds to the first nuclear division. These first two furrows apparently represent the first two meridional furrows of the holoblastic egg though in the Elasmobranch the first to appear may be either a or (3. More usually, in place of a second regular furrow developing, irregular branches of the first furrow, or even independent furrows, appear and an arrangement of somewhat radiating furrows is brought about which gradually becomes converted into a network (Fig. 8, B, C, D). It should be noticed in regard to these segmentation furrows. 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 MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
Size: 1590px × 1571px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
