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 212 C'CELENTERATA. beset with eight meridional rows of vibratile plates, which, working like oars, serve for locomotion (fig. 155). The body parenchyma in the Sponges consists principally of amoeba-like cells, which frequently bear flagella, but which never produce stinging threads. In the Cnidaria (Polypa and Medusas), in certain cells the peculiar struc- tures known as thread cells (fig. 156 )are developed. They cons
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 212 C'CELENTERATA. beset with eight meridional rows of vibratile plates, which, working like oars, serve for locomotion (fig. 155). The body parenchyma in the Sponges consists principally of amoeba-like cells, which frequently bear flagella, but which never produce stinging threads. In the Cnidaria (Polypa and Medusas), in certain cells the peculiar struc- tures known as thread cells (fig. 156 )are developed. They consist of small capsules filled with fluid, and containing a sharp-pointed, spi- rally coiled thread; they are developed in cells which may be called cnido- blasts. Under cer- tain mechanical conditions, under influence of the pressure pro- duced by contact with a foreign body, these cap- sules burst, and the thread is sud- denly protruded, and either fastens on to the cause of disturbance or pierces it, carrying PIG. 156. — Ncuwtocysts and Fir,, in'. — r>ippe (Hormiphora) \r.^rt 'f 4- f cnidoblasts of Biphonophora. plumosa (after Chun). O, a and 6, with the cnidocil mouth. the fluid Contents of the cell, c to e, Nemato- c .-, cysts with evaginated thread. or the capsule. In many parts of the body, and especially on the tentacles, which serve for the capture of prey, these small microscopic weapons are collected in masses, and are often united in a peculiar arrangement to form batteries of thread cells.
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