The function of these layers appears to be primarily protective. Structure for XPA domains involved in binding to DNA and RPA is solved [51, 52]. 7. In the cytoplasm is present both rough and smooth surfaced endoplasmic reticulum. The thread either sticks to the prey (glutinants), or coils around its bristles (volvents), or it penetrates its body (penetrants), and injects a powerful toxin which paralyses even such large animals as a water-flea or small worms. Large membrane bounded vacuoles are found in the cytoplasm, the vacuoles of the apical region may represent digestive vacuoles, the vacuoles of the basal region may represent residual bodies containing undigested food material. Germ cells originate by the repeated divisions of the interstitial cells in certain restricted regions of the body of Hydra during the summer. Hydra principle requires a well structured fleet for proper execution. Margaret_Rogers. Answer Now and help others. In between the outer epidermis and inner gastro dermis, a thin non-cellular layer of jelly-like substance called mesogloea is present. A few small membrane bound vesicles are present immediately below or connected to plasma membrane. Digestive cells of tentacles are pyramidal in shape and contain a large intracellular space surrounded by a thin rim of cytoplasm in which lipid droplets and food vacuoles are found. An anaesthetized Hydra will discharge its nematocysts in the usual way when stimulated; even nematocysts removed from the body will shoot out their thread if an adequate stimulus is applied to them. Illustration of contour, educational, anatomy - 162611403 These are small, oval or round cells with a large nucleus. Finally, cell attachments break. 3. 4. In the autumn, testes appear near the tentacles and ovaries near the base. They are interspersed singly between the digestive cells. 31.6) lying in groups. Free ribosomes are abundant in the cytoplasm. The apices of the three stylets lie close to each other but their bases are turned outwardly. Nerve nets connect sensory photoreceptors and touch-sensitive nerve cells located in the body wall and tentacles. In discharge of a nematocyst the operculum opens, water enters the capsule, the tube is turned inside out and shot out with a force, the eversion causes the spines to come to the outer surface of the tube. A sensory cell acts both as a receptor and as a sensory neuron, that is, it both receives and transmits impulses. The mucous granules are spherical about 0.5 to 1.0 µ in diameter and contain finely granular material. Body differentiated into a long tubular trunk and a hypostome or mouth surrounded by a ring of long tentacles. 31.12B) is situated perpendicular to the long axis close to the apices of epithelial cells. Share Your PPT File. Hydra are freshwater organisms, only a few millimeters in length, and belong to the phylum Cnidaria, which also includes jellyfish and coral. The spines are small and more than 50 in number. One or more Golgi apparatus is found near the nucleus and is surrounded by the rough-surfaced endoplasmic reticulum. The secondary structures within the zinc-finger containing region and the C-terminal domain are well described with characterization of the DNA- and RPA-binding sites . 31.3) of Hydra shows a central cavity in its body called coelenteron (= hollow gut) functionally referred to as gastro vascular cavity. The Golgi apparatus is small and lies close to the nucleus. Figure 2.3.2. shows the schematic structure of a diaphragm bellows as a diagram as well as a typical diaphragm bellows in the form of a metallo-graphic cut. It is a continuous layer which extends over both body and tentacles, thickest in the stalk portion and thinnest on the tentacles. Some granular epidermal cells of the basal disc secrete a gas to form a bubble by which the Hydra breaks from its attachment and is lifted up. 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