. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 260 R. AND K. OSANAI. Figure 1. Normal larvae of .l\tcrnui pcclinilcru. (A) start of gastru- lation; (B) early gastrula stage: (Cl mesenchyme-differentiation stage; (D) late gastrula stage; (E. F) mouth-formation stage; and (G, H) bipin- naria stage. (E, G) Observed from dorsal side. (F, H) Observed from right side, ac = anterior coelom. pc = posterior coelom, e = esophagus, s = stomach, i = intestine. Scale bar = 100 ^m. outer layer became flattened slightly in a dorso-ventral direction (Fig. ID). Mouth-formation
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 260 R. AND K. OSANAI. Figure 1. Normal larvae of .l\tcrnui pcclinilcru. (A) start of gastru- lation; (B) early gastrula stage: (Cl mesenchyme-differentiation stage; (D) late gastrula stage; (E. F) mouth-formation stage; and (G, H) bipin- naria stage. (E, G) Observed from dorsal side. (F, H) Observed from right side, ac = anterior coelom. pc = posterior coelom, e = esophagus, s = stomach, i = intestine. Scale bar = 100 ^m. outer layer became flattened slightly in a dorso-ventral direction (Fig. ID). Mouth-formation stage extended from 40 to 48 h, dur- ing which time the body became much more flattened in a dorso-ventral direction. The blastopore decreased in di- ameter and moved to the ventral side (Fig. 1F). A pair of coelomic rudiments projected to the lateral side from the tip of the archenteron (Fig. IE). The outer diameter of the posterior ;4 Oi" the rest of the archenteron started to increase gradually. A rudiment of the left posterior coelom projected into the blastocoel from the dorsal wall of this widening region and began to migrate to the left side (Fig. IF). The archenteron began to bend toward the ventral side, where invagination of the stomodaeum had already begun. Larvae reached the early bipinnaria stage at about 72 h. The digestive tract had differentiated into the esoph- agus, stomach, and intestine. The boundary between the esophagus and stomach was sharply constricted by the cardiac sphincter. The boundary between the stomach and intestine was not so obviously constricted by the py- loric sphincter compared to that of sea urchins. Coeloms existed on both sides of the esophagus and by the left side of the stomach (Fig. 1G). Cellular volume of archenteron In sea urchins, translocation of cells from the outer layer into the archenteron wall occurs only in the first few hours of gastrulation (Horstadius. 1973; Hardin, 1989; Burke el ai, 1991). To clarify whether this
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
