. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GASTRULATION IN SAND DOLLAR 289 F ^zZ&. Figure 1. Processes of gastiulation in Hcmii'cntn> pulchenimus and Scuphirhiiiiu mimhilis. Embryos of both species were cultured at 18°C and observed hourly. Embryos were embedded in Spurr resin. (A-F) H. pulcherrimus, 17-22 h. (G-L) S. mimhilis, 14-19 h. In H. pulcherrimus embryos, the primary and secondary invagination is clearly distinguished by the presence of a pause in the archenteron elongation (C-D. 1-2 hours). After the occurrence of the secondary invagination. the
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GASTRULATION IN SAND DOLLAR 289 F ^zZ&. Figure 1. Processes of gastiulation in Hcmii'cntn> pulchenimus and Scuphirhiiiiu mimhilis. Embryos of both species were cultured at 18°C and observed hourly. Embryos were embedded in Spurr resin. (A-F) H. pulcherrimus, 17-22 h. (G-L) S. mimhilis, 14-19 h. In H. pulcherrimus embryos, the primary and secondary invagination is clearly distinguished by the presence of a pause in the archenteron elongation (C-D. 1-2 hours). After the occurrence of the secondary invagination. the archenteron became slender. In S. mimbilis embryos, the archenteron invaginated contin- uously, and the diameter of the archenteron remained unchanged during gastrulation. The scale bar indicates 50 /xm. attachment. The processes of gastrulation were photo- graphed at intervals of 10 min. Results Morphological changes during gastrulation Figure 1 shows the processes of gastrulation in embryos of H. pulcherrimus (A-F) and S. mirabilis (G-L) kept at 18°C. In a regular echinoid, H. pulcherrimus, primary (Fig. 1A-C) and secondary invagination (Fig. 1D-F) were clearly distinguished by the presence of a time lag in archenteron elongation (1-2 h. Fig. 1C-D). On the other hand, the archenteron of S. mirabilis embryos elongated at a constant rate during the course of invagination (Fig. 1G-L). Besides archenteron elongation, several differences were noticed in the morphology of the embryos of these two species. In H. pulcherrimus, the height of the embryo in- creased to some extent during primary invagination. After the onset of secondary invagination, the embryos were shortened along the animal-vegetal axis (Fig. 2A). The width of the embryos increased as gastrulation progressed (Fig. 2B). This was caused by the expansion of the ecto- dermal layer, especially at the lateral blastocoel wall (Fig. 2C). In contrast, S. mirabilis embryos became shorter as invagination progressed (Fig. 2D)
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
