Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 212 CCELENTERATA. beset with eiglit meridional rows of vibratile plates, which, working like oars, serve for locomotion (fig. 155). The body parenchyma in the Sponges consists principally of arareba-like cells, which frequently bear flagella, but which never produce stinging threads. In the Cnidaria (Polyps and Medusae), in certain cells the peculiar struc- tures known as thread cells (fig. 15 G )arc developed. They consist of small cap
Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 212 CCELENTERATA. beset with eiglit meridional rows of vibratile plates, which, working like oars, serve for locomotion (fig. 155). The body parenchyma in the Sponges consists principally of arareba-like cells, which frequently bear flagella, but which never produce stinging threads. In the Cnidaria (Polyps and Medusae), in certain cells the peculiar struc- tures known as thread cells (fig. 15 G )arc 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 -Cy3!ppe (RormipUra) -^^.^ j^ ^ ^^^^^ ^j the fluid contents of the capsule. In many parts of the body, and especially on the tentacles, which serve for the cajiture of prey, these small micro.'ccpic weapons are collected in masses, and are often united in a peculiar arrangement to form batteries of thread cells.
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