. A manual of elementary zoology . Zoology. 184 MANUAL OF ELEMENTARY ZOOLOGY definition which of the repeated structures we call indi- viduals. Other kinds of polyps and medusas are known than those coeienterata wnich are represented by Hydra and Obelia. Sea-anemones (Actiniaria) are polyps (Fig. 397) of rather complex structure, the edge of the mouth being tucked in to form a gullet lined with ectoderm, while folds or mesenteries of endoderm stretch across the enteron from. 7KZLS? Fig. 116.—A diagram of a vertical section of a sea-anemone. ect., ectoderm of tentacle ; , ectoderm lining
. A manual of elementary zoology . Zoology. 184 MANUAL OF ELEMENTARY ZOOLOGY definition which of the repeated structures we call indi- viduals. Other kinds of polyps and medusas are known than those coeienterata wnich are represented by Hydra and Obelia. Sea-anemones (Actiniaria) are polyps (Fig. 397) of rather complex structure, the edge of the mouth being tucked in to form a gullet lined with ectoderm, while folds or mesenteries of endoderm stretch across the enteron from. 7KZLS? Fig. 116.—A diagram of a vertical section of a sea-anemone. ect., ectoderm of tentacle ; , ectoderm lining gullet; end., endoderm; ent., enteron ;g., gullet ; gon., gonad ; , ^I mesenterial filament; mus., longitudinal or "retractor" muscle; mus'., oblique or "parietal" muscle ; , mesoglea ; ten., tentacle; i°mes., primary mesen- tery. the body - wall, some of them {primary mesenteries) reaching the gullet. The testes and ovaries are developed from the endoderm of the mesenteries, and their products are shed through the mouth. The ectoderm is ciliated, and the mesoglea contains cells of various kinds derived from the ectoderm and At the ends of the 1 Though these cells do not form a third layer or " mesoderm " such as is found in the higher animals (p. 230), yet they foreshadow that element of the mesoderm which is known during development as "mesenchyme" (p. 495).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Borradaile, L. A. (Lancelot Alexander), 1872-1945. London : H. Frowde, Hodder & Stoughton
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