. Animal physiology. Physiology, Comparative; Physiology, Comparative. 246 RESPIRATION IN MOLLUSCA. these animals usually reside in the water, or only quit it occa- sionally, there are some species, known under the name of land- crabs, which have the power of living for some time at a dis- tance from water. In order to prevent their gills from drying up, which would destroy their power of acting on the air, there is a kind of spongy structure in the gill-chamber, by which a fluid is secreted, that keeps them constantly moist. 316. In the Mollusca we find the gills arranged in a great variety o
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 246 RESPIRATION IN MOLLUSCA. these animals usually reside in the water, or only quit it occa- sionally, there are some species, known under the name of land- crabs, which have the power of living for some time at a dis- tance from water. In order to prevent their gills from drying up, which would destroy their power of acting on the air, there is a kind of spongy structure in the gill-chamber, by which a fluid is secreted, that keeps them constantly moist. 316. In the Mollusca we find the gills arranged in a great variety of modes. In the lowest class, the Tunicata, the respi- ratory membrane is merely the lining of the large chamber formed by the mantle, through which a stream of water is con- tinually made to flow (§. 319) ; and this surface is sometimes extended, by the folding or plaiting of the membrane. In most. Fig. 142.—Anatomy of the Oyster. v, one of the valves of the shell; v', its hinge ; m, one of the lobes of the mantle ; m', a portion of the other lobe folded back; e, muscles of the shell; br, gills; b, mouth ; t, tentacula, or prolonged lips ; /, liver; i, intestine; a, anus ; co, heart. of the Conchifera, however, we find four lamella? or folds of membrane (br, Fig. 142), lying near the edge of the shell, and copiously supplied with blood-vessels. In the Oyster, these are freely exposed to the surrounding element, the lobes of the mantle being separated along their entire length ; but where. 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 Carpenter, William Benjamin, 1813-1885. London : Wm. S. Orr and Co.
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