. Analysis of development. Embryology; Embryology. 374 Special Vertebrate Organogenesis the observation that isolated sections of the spinal cord, transplanted to the flank, where they are deprived of axial stretch, do become much thicker and shorter than if they had developed in continuity with the rest of the cord (Zacharias, '38). The ease with which lateral halves of the cord are regenerated with the participation of transverse cell shifts from the intact half (Detwiler, '47b; Harrison, '47; Holtzer, '51), contrasted with the failure to repair major gaps in the longi- tudinal direction, li
. Analysis of development. Embryology; Embryology. 374 Special Vertebrate Organogenesis the observation that isolated sections of the spinal cord, transplanted to the flank, where they are deprived of axial stretch, do become much thicker and shorter than if they had developed in continuity with the rest of the cord (Zacharias, '38). The ease with which lateral halves of the cord are regenerated with the participation of transverse cell shifts from the intact half (Detwiler, '47b; Harrison, '47; Holtzer, '51), contrasted with the failure to repair major gaps in the longi- tudinal direction, likewise indicates the tivity declines at some levels and flares up at others. Moreover, the centers of proliferation often form a quiltlike pattern with foci at the intersections of four longitudinal columns with transverse bands (neuromeres) (Berg- quist and Kallen, '54). Some of the segmental peaks coincide with the appearance of promi- nent peripheral organs in the corresponding sector, for instance, in the limb segments. As will be shown later (p. 381), part of this correspondence is due to an active control ex- erted upon the centers by their respective. 5 lO IS Fig. 140. Mitotic pattern of the brain of Amblystoma (after Burr, '32). A, Earlier stage (31, after Harri- son). B, Later stage. (35, after Harrison). To facilitate comparison, the two stages are represented side by side in symmetrical arrangement. The outline of the brain is indicated. Horizontal lines express the number of mitotic figures contained in serial brain slices of 30/i each. Abscissa: Number of mitoses. Full black: Mitoses in forebrain and hypothalamus. Individual bars: Mitoses in the rest of the brain. Brackets indicate position and extent of sensory placodes. Note the change in the distribution of peaks from A to B. need of extraneous stretch for elongation. In the brain, the hydrostatic turgor deserves similar attention as a potential regulator of the expanse of the proliferative surface, hence of the
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
