. Text-book of embryology. Embryology. 296 INVEETEBEATA CHAP. The division of the apical cells Iq^" results in the formation of a well- marked plate of eight centraL-eells at the animal pole (Fig. 231).. Fia. 229.—Two stages in the gastrulation oi Patella coerulea in optical longitudinal section. The residual macromeres are shaded. (After Wilson.) A, stage showing the formation of the mesoderm mother cell, 4d, and the inward migration of the macromere, 3D. B, stage showing the division of the left mesoderm mother cell, and the inward migration of the other macromeres. ap, apical plate ; p
. Text-book of embryology. Embryology. 296 INVEETEBEATA CHAP. The division of the apical cells Iq^" results in the formation of a well- marked plate of eight centraL-eells at the animal pole (Fig. 231).. Fia. 229.—Two stages in the gastrulation oi Patella coerulea in optical longitudinal section. The residual macromeres are shaded. (After Wilson.) A, stage showing the formation of the mesoderm mother cell, 4d, and the inward migration of the macromere, 3D. B, stage showing the division of the left mesoderm mother cell, and the inward migration of the other macromeres. ap, apical plate ; , prototroch. Meanwhile other, changes take place. The four groups of primary trochoblasts develop transverse rows of power- ful cilia, each row bearing a striking resemblance to a single "comb" of a Ctenophore, and the apical cells develop a terminal tuft of long stiff cilia. The embryo at this stage, when looked at from above (Fig. 330), bears a striking resem- blance to a larval Cteno- phore; and this stage, which is reached eight hours after fertilization, is termed by Wilson the Ctenophore stage. The cells constituting the apical plate do not appear to divide further, but the cells forming the arms of the Molluscan cross under- go repeated divisions, in consequence of which these arms cease to be. 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: 2195px × 1139px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
