. A manual of elementary zoology . Zoology. HYDRA AND OB ELI A. POLYPS AND MEDUSA 163 animal to the surface it hangs from. Each mus- culo-epithelial cell has a large oval nucleus. In the tentacles these cells are less tall than elsewhere. Between the narrow ends of the musculo-epithelial cells are spaces, which are filled with small, rounded inter- stitial cells. These form a reserve from which, in various circumstances, any of the other cells of the body can arise. Thus they retain the undiffer- entiated nature of the germs and are sometimes called indifferent cells. Embedded in the con- tinu
. A manual of elementary zoology . Zoology. HYDRA AND OB ELI A. POLYPS AND MEDUSA 163 animal to the surface it hangs from. Each mus- culo-epithelial cell has a large oval nucleus. In the tentacles these cells are less tall than elsewhere. Between the narrow ends of the musculo-epithelial cells are spaces, which are filled with small, rounded inter- stitial cells. These form a reserve from which, in various circumstances, any of the other cells of the body can arise. Thus they retain the undiffer- entiated nature of the germs and are sometimes called indifferent cells. Embedded in the con- tinuous layer of the ecto- derm are peculiar cells known as cnidoblasts. These are very numerous in the tentacles, where they lie in groups or batteries (Figs. 102, 403), but absent from the basal disc. Each of them has a pear-shaped body with the narrow end at the surface of the animal, where there projects from it a short process known as the cnidocil. On this side the cell contains a pear-shaped sac, called the nematocyst. The narrow outer end of the sac is tucked in and. FIG. 102.—A diagrammatic, longitudinal section of Hydra, magnified.—From Shipley and MacBride. bat., Battery of nematocysts. Only a few of these are shown; they cover the tentacles; ect., ectoderm; end., endoderm; ent., en- teron ;_/!, foot; , hollow of a tentacle \ov., ovary ; , structureless lamella; t. 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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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1920
