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Various stages in the development of Phallusia mammillata

Organism : Ascidian
Species : Phallusia mammillata
Description : Various stages in the development of Phallusia mammillata. (From Huxley; after Kowalevsky.)  The embryos are represented in longitudinal vertical section.  I. Commencing gastrula stage. fh. segmentation cavity.  II. Late gastrula stage with flattened dorsal surface. eo. blastopore; ch. notochord; dd. hypoblast.  III. A more advanced embryo with a partially-formed neural tube. ch. and dd. as before; n. neural tube; c. epiblast.  IV. Older embryo in which the formation of the neural tube is completed. dd. hypoblast enclosing persistent section of alimentary tract; dd´. hypoblast in the tail; m. muscles.  V. Larva just hatched. The end of the tail is not represented. a. eye; gb. dilated extremity of neural tube with otolith projecting into it; Rg. anterior swelling of the spinal division of the neural tube; f. anterior pore of neural tube; Rm. posterior part of neural tube; o. mouth; Chs. notochord; kl. atrial invagination; dd. branchial region of alimentary tract; d. commencement of œsophagus and stomach; dd´. hypoblast in the tail; m. muscles; hp. papilla for attachment.  VI. Body and anterior part of the tail of a two days’ larva. klm. atrial aperture; en. endostyle; ks. branchial sack; 1ks. 2ks. branchial slits; bb. branchial vessel between them; ch. axial portion of notochord; chs. peripheral layer of cells. Other reference letters as before.
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Tags : Gastrula Embryo Larva Development Notochord Tail
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