内容非常全面-两栖动物百科全书.pptVIP

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Respiratory System Adult frogs lose the gills but can respire in three ways: through the lungs, through the skin, and through the mouth. Respiration through the lungs is called pulmonary respiration. A frog breathes by changing the volume and pressure of air in its mouth while either opening or closing its nostrils Respiratory System Air moves from the throat to the lungs through a slit-like passage called the glottis. Because the frogs lungs are small, cutaneous respiration, or respiration through the skin in both air and water, is very important, especially during estivation or hibernation. Oxygen can diffuse across the lining of the mouth and into the blood. Frogs use mouth breathing for only a relatively small amount of their respiration.        Excretory System Urine and wastes from the digestive system are eliminated through the anus. When a frog is in water, its permeable skin allows the water to enter its body. Frogs that live primarily in water rid themselves of excess water by excreting a large volume of very dilute urine. Frogs that live mainly on land conserve water by producing a small volume of more concentrated urine. Excretory System Amphibians eliminate two primary types of metabolic waste products—carbon dioxide from respiration and waste com-pounds from the breakdown of foods. Are the primary excretory organs and lie on either side of the spine against the dorsal body wall. The kidneys filter nitrogenous wastes from the blood The Nervous System The frog brain is more complex than the fish brain, enabling the frog to contend with a more varied environment. The optic lobes, which control vision, lie behind the cerebrum. The cerebellum, a small band of tissue lying at right angles to the long axis of the brain, is the center of balance and coordination. Nervous System The medulla oblongata lies at the back of the brain and joi