. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. St. 1 Si. 2 SI. .1 SI. 4 SI. 1 SI. 2 Si. 3 Stage in early phase of imagination St. 4 Figure 6. Frequency of the appearance of columnar, skewed, and wedge-shaped cells during gastrulation: Hemicentrotus pit/cherriinus (A. B); Scai'hi'cliinin mirabilis (C, D). (A. C) Animal hemisphere. IB. D) Vegetal hemisphere. Columnar cells (solid lines) are more abundant in the animal hemisphere. Skewed cells (dotted lines) were observed more fre- quently in S. mirabilis. In both species, the population of columnar cells increased as the g
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. St. 1 Si. 2 SI. .1 SI. 4 SI. 1 SI. 2 Si. 3 Stage in early phase of imagination St. 4 Figure 6. Frequency of the appearance of columnar, skewed, and wedge-shaped cells during gastrulation: Hemicentrotus pit/cherriinus (A. B); Scai'hi'cliinin mirabilis (C, D). (A. C) Animal hemisphere. IB. D) Vegetal hemisphere. Columnar cells (solid lines) are more abundant in the animal hemisphere. Skewed cells (dotted lines) were observed more fre- quently in S. mirabilis. In both species, the population of columnar cells increased as the gastrulation proceeded (A. C). Wedge-shaped cells (tiro- ken lines) appear sparsely in the animal hemisphere. In contrast, the most abundant type of cells are wedge-shaped cells in the vegetal halves (B. D). Columnar cells were rarely observed in S. mirtihilis. but such cells in- creased in H. pulclierriinii* after the secondary imagination had started. H. /ntlclwrrinnis embryos were stretched along the axis of the archenteron (Fig. 9A-D). After the completion of the secondary invagination. the cells resumed a cuboid shape (Fig. 9E-F). In contrast, the cells in the archenteron of 5. mirabilis embryos were not stretched at any stage of later invagination (Fig. 9G-L). It should be noted that the cells near the blastopore were elongated along their apico-basal direction through all the stages examined. These changes in cell shape were quantified according to the methods described by Hardin (1988); two ratios, YIX (ratio of lengths along and perpendicular to the axis of the archenteron) and L/W (ratio of cell length and width) were obtained (Fig. 10). Both YIX and L/W increased during the secondary invag- ination in H. pulcherrimus embryos, and decreased to the initial level at the end of secondary invagination (Fig. 10A). On the other hand, the ratios did not change in S. mirabilis embryos through these stages of invagination (Fig. 10B). The result clearly shows that the archentero
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
