. Outlines of zoology. Zoology. 146 CCELENTERA. of hollow tentacles around the oral disc; the mouth is usually a longitudinal slit. The tentacles are contracted when the animal is irritated, and the whole body can be much reduced in size. Just below the margin of the oral disc there is a powerful sphincter muscle; this contracts, and pulls together the body-wall over the mouth and retracted tentacles. Water may pass out gently or otherwise by a pore at the tip of each tentacle, and long white threads, richly covered with stinging cells, can be ejected in many anem- ones through the walls of th
. Outlines of zoology. Zoology. 146 CCELENTERA. of hollow tentacles around the oral disc; the mouth is usually a longitudinal slit. The tentacles are contracted when the animal is irritated, and the whole body can be much reduced in size. Just below the margin of the oral disc there is a powerful sphincter muscle; this contracts, and pulls together the body-wall over the mouth and retracted tentacles. Water may pass out gently or otherwise by a pore at the tip of each tentacle, and long white threads, richly covered with stinging cells, can be ejected in many anem- ones through the walls of the body (Fig. 64). General structure.— The Anthozoon polype differs markedly from the Hydroid polype— not only because an invagination from the oral disc inwards has formed a gullet tube, which hangs down into the general cavity, but also because a number of partitions or mesen- teries extend from the body wall towards this gullet. Some of the partitions are " com- plete," they reach the gullet; others are " incomplete," do not extend so far inwards. The complete mesenteries are attached to the oral disc above, to the side of the gullet, and to the base, and all the mesenteries are in- growths of the body wall. The cavity of the anemone is thus divided into a number (some multiple of six) of radial chambers. These are in communication at the base,. Fig. 64.—Vertical section of a sea- anemone.—After Andres. i., Tentacles ; o., mouth ; a?s., oesophagus ; c, c'.t apertures through a mesentery; a., a'., acontia; g., genital organs on mesentery ; , mesen- teric filaments; ?;?./., longitudinal muscles; s., primary septum or mesentery; s'., second- ary septum; /'., tertiary septum; v., basal 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 Thomson, J. Arthur (John Arth
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
