. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 18 M. J. KATZ J**^, . •, -.^* « i "• IS^^J&. FIGURE 15. Electron micrograph of an atrial primordium in the lateral wall of the tadpole body. AT = atrial primordium, EP = epidermis, G = gut primordium. Bar = 10 j/m. mordia are smooth. During metamorphosis, the two atrial primordia fuse and form the single atrial siphon of the adult (Berrill, 1950). For a general description of the development of the atria, see Willey (1893a). 3. Gut primordium In the 19-20h tadpole, the gut primordium is a closed folded tube, one cel
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 18 M. J. KATZ J**^, . •, -.^* « i "• IS^^J&. FIGURE 15. Electron micrograph of an atrial primordium in the lateral wall of the tadpole body. AT = atrial primordium, EP = epidermis, G = gut primordium. Bar = 10 j/m. mordia are smooth. During metamorphosis, the two atrial primordia fuse and form the single atrial siphon of the adult (Berrill, 1950). For a general description of the development of the atria, see Willey (1893a). 3. Gut primordium In the 19-20h tadpole, the gut primordium is a closed folded tube, one cell thick, that fills the ventral two-thirds of the body (Figs. 2, 4, 15, 16). The gut lumen (the "endodermal cavity') extends from the pharyngeal primordium rostrally to the head of the notochord caudally. The gut primordium is followed in the tail by the 'endodermal strand'—a lumenless set of gut cells, in single file, lying directly under the notochord along its entire length (Figs. 2, 7, 8). The prosencephalon lies directly along the top wall of the gut primordium. In the rostral half of the tadpole body, the bottom wall of the gut primordium lies directly along the ventral epidermis. The rostral end of the gut primordium borders an extracellular space behind the adhesive organ. This space is called the 'pre-oral lobe'; it contains separated spherical cells and will apparently continue to fill with cells before metamorphosis (Willey, 1893a). Cells of the gut primordium and of the endodermal strand are roughly cuboidal (4-8 /im wide) and are characterized by large numbers of yolk vesicles. The cyto- plasm of these cells appears "loose" and vacuolated and contains few organelles. At 19-20 h, the luminal surfaces of the gut cells are irregular but have neither cilia nor extensive microvilli. At this developmental stage, there do not appear to be any specialized gland cells. 4. Mesodermal pockets The 19-20 h Ciona tadpole contains a number of pockets of meso
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
