. Elementary biology; an introduction to the science of life . Fig. 45. How the lobster breathes The featherlike gills of these crustaceans are protected by an extension of shell which incloses them almost completely. By the action of appendages connected with the mouth organs a constant current of water is made to pass over the gills through the space under the shield, moving from the back edge forward is found in such animals as the earthworm. In this the respi- ration takes place by osmosis through the moist epidermis, or skin. In some worms there are extensions of the skin surface into lit
. Elementary biology; an introduction to the science of life . Fig. 45. How the lobster breathes The featherlike gills of these crustaceans are protected by an extension of shell which incloses them almost completely. By the action of appendages connected with the mouth organs a constant current of water is made to pass over the gills through the space under the shield, moving from the back edge forward is found in such animals as the earthworm. In this the respi- ration takes place by osmosis through the moist epidermis, or skin. In some worms there are extensions of the skin surface into little outgrowths, called gills. In clams and oysters there are special outgrowths that multiply the breathing surface in much the same way (Fig. 44). In the lobster, crab, crayfish, and related animals there are special structures in which there is a great deal of surface in a comparatively small space, crowded together in a particular region of the body (Fig. 45). When we come to animals with backbones, we find that the breathing organs are connected with the food pipe, so that all of them can, and many of them do, breathe through the
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