Amphibians - PowerPoint PPT Presentation
Thank you for your feedback. You can use PowerShow. Mouth is terminal, slitlike aperture bounded by horny Jaws. Long-toed Salamander Thurston Road, ponds at W. Previous page Circulatory system. At the end of pyloric stomach a small constriction is present. The tongue of the amphibians is provided with a viscosity that makes it very sticky.

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How is the Amphibian Digestive System?

Prior to the evolution of the metanephric kidney, the products of the male gonad , the testis, traveled through the same duct with the nitrogenous wastes from the kidney. But with the appearance of the metanephros , the two systems became separated.

The female reproductive system never shared a common tube with the kidney. Oviducts in all female vertebrates arise as separate tubes with openings usually near, but not connected to, the ovaries.

The oviducts, like the Wolffian ducts of the testes , open to the cloaca. Both ovaries and testes lie in the body cavity near the kidneys. With the evolution of the reptilian egg , internal fertilization became necessary. The males of all modern reptiles, with the exception of tuatara , have functional copulatory organs.

Unlike the penis of turtles and crocodiles, the copulatory organ of lizards and snakes is paired, with each unit being called a hemipenis. The hemipenes of lizards and snakes are elongated tubular structures lying in the tail. Completion of the erection is brought about by blood filling the sinuses in the erectile tissue.

Only one hemipenis is inserted into a female, but which one is a matter of chance. Unlike the penis of mammals, the copulatory organs of reptiles do not transport sperm through a tube. The ducts from the testes, as already mentioned, empty into the cloaca, and the sperm flow along a groove on the surface of the penis or hemipenis. In general construction the eyes of reptiles are like those of other vertebrates.

Accommodation for near vision in all living reptiles except snakes is accomplished by pressure being exerted on the lens by the surrounding muscular ring ciliary body , which thus makes the lens more spherical. In snakes the same end is achieved by the lens being brought forward.

The lens moves as a result of the pressure built up on the vitreous humour by contractions of muscles located at the base of the iris. The pupil shape varies remarkably among living reptiles, from the round opening characteristic of all turtles and many diurnal lizards and snakes to the vertical slit of crocodiles and nocturnal snakes and the horizontal slits of a few tree snakes.

Undoubtedly the most bizarre pupil shape is that of some geckos , in which the pupil contracts to form a series of pinholes, one above the other. The lower eyelid has the greater range of movement in most reptiles. In crocodiles the upper lid is more mobile. Snakes have no movable eyelids, their eyes being covered by a fixed transparent scale.

Visual acuity varies greatly among living reptiles, being poorest in the burrowing lizards and snakes which often have very small eyes and greatest in active diurnal species which usually have large eyes.

Judging by the size of the skull opening in which the eye is situated, similar variation existed among the extinct reptiles. Extinct forms, such as the ichthyosaurs, that hunted active prey had large eyes and presumably excellent vision; many herbivorous types, such as the horned dinosaur Triceratops , had relatively small eyes and weak vision. Colour vision has been demonstrated in few living reptiles. We welcome suggested improvements to any of our articles.

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How Do Amphibians Digest Their Food?