. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. AMAROECIUM CONSTELLATUM. II 67 or tadpole has been described thoroughly by Grave (1921) and shall be presented here in brief summary since reference to it is necessary. A short description of the external appearance of these stages will be given first and referred to in subsequent treatment of organogenesis as Stages I, II, III, and IV. The terms, larval action system and adult action system, used by Grave (1935, 1944) will be adopted for the structures functioning during larval life and those functioning during adult life r
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. AMAROECIUM CONSTELLATUM. II 67 or tadpole has been described thoroughly by Grave (1921) and shall be presented here in brief summary since reference to it is necessary. A short description of the external appearance of these stages will be given first and referred to in subsequent treatment of organogenesis as Stages I, II, III, and IV. The terms, larval action system and adult action system, used by Grave (1935, 1944) will be adopted for the structures functioning during larval life and those functioning during adult life respectively. The tail bud stage By the end of gastrulation the embryo is approximately spherical except for a shallow postero-ventral invagination of the ectoderm constricting tail from trunk region. The furrow appearing first on the right side is deeper there, and less deep as it extends to the left side. The tail bud is short and rounded, curving immedi- ately toward the ventral side of the trunk. Through the thin epidermis quadruple rows of large muscle cells can be seen lying dorsal and ventral to the notochord. The neural plate is elevated at the periphery to form the neural groove, enclosing; anteriorly a wide depression, the presumptive brain region, posteriorly a narrow, trough-like depression lying to the left of the notochord, the presumptive neural tube (Fig. I A). FIGURE 1. A. Stage I, embryo before neural folds close. 160 X. B. Stage II, early tad- pole; beginning of differentiation of digestive and nervous systems. 160 X. b. v., brain vesicle; d. ph., dorsal diverticulum of pharynx; m. bd., muscle band; n. t., neural tube; ph., pharynx; y. m., yolk mass. A transverse section through the tail bud stage discloses that the embryo is solid. A single layer of definitive endoderm lies under the concave neural plate (Fig. 5£). This layer of cells develops from the cells that form the superficial "pseudo- invagination" cavity of gastrulation. The depressio
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
