Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote . elementarytextbo01clau Year: 1892-1893 CsJi FIG. 113.—Development of the planula of Chrysaora to the Scyphisturua sta^o, with eight arms, a, Two layered planula with a narrow gastric cavity; 4, the same after its attachment with just-formed mouth (O), and commencing tentacles; c, four-armed Scy- phistoma polyp ; Csh, excreted cuticular skeleton ; d, eight-armed Scyphistoma polyp with wirle mouth; If, longitudinal muscles of the gastric ridges; dk, excrete
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote . elementarytextbo01clau Year: 1892-1893 CsJi FIG. 113.—Development of the planula of Chrysaora to the Scyphisturua sta^o, with eight arms, a, Two layered planula with a narrow gastric cavity; 4, the same after its attachment with just-formed mouth (O), and commencing tentacles; c, four-armed Scy- phistoma polyp ; Csh, excreted cuticular skeleton ; d, eight-armed Scyphistoma polyp with wirle mouth; If, longitudinal muscles of the gastric ridges; dk, excreted cuticular skeleton. which is directed forward in swimming, and acquires at its free ex- tremity a new mouth, round which 1, 2, 4, 8, and finally 16 long tentacles soon make their appearance; while the broad oral region projects as a contractile cone (fig. 113 b, c, d}. Inside the gastric cavity there project four gastric ridges with longitudinal muscular bands extending from the foot or point of attachment to the base of the oral cone. When the polyp, which has now become a Scyphis- toma, has under favourable conditions of nutrition reached a certain size (about 2 to 4 mm.), ring-like constrictions are formed at the
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