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| Respiratory, Excretory, Nervous and Reproductive System of Frog |
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| It consists of a pair of lungs, a pair of bronchi and a trachea. The lungs contain numerous microscopic functional units called alveoli. |
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| These structures are involved in pulmonary respiration. In addition, there is buccal respiration, through the buccal cavity and cutaneous respiration through the moist skin. |
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| Respiratory System |
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| It is represented by a pair of kidneys, a pair of ureters and a urinary bladder. Kidney contain numerous units called nephrons which filter blood, remove urea and convert it into urine. It is collected in the urinary bladder through ureters (kidney ducts), temporarily stored and then periodically eliminated. |
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| The excretory system become closely associated with the reproductive system, particularly in the males. The two systems together represent the urinogenital system. |
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| Excretory System |
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| It is represented by a brain, a spinal cord, cranial nerves, spinal nerves and the autonomic (sympathetic and parasympathetic) nerves. |
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| Brain and spinal cord together form the central nervous system. Brain consists of a pair of olfactory lobes, a pair of cerebral hemispheres, a pineal body, a pair of optic lobes a cerebellum and a medulla oblongata. The spinal cord extends from medulla oblongata up to the tip of the trunk. |
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| Ten pairs of cranial nerves arise from the brain and innervate the different parts of the body. Ten pairs of spinal nerves arise from the spinal cord and supply to different parts of the body. The autonomic nerves are formed by two strands of nerves one on either side and parallel to the spinal cord. |
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| In frog sexes are separate. Male and female frogs can be morphologically distinguished. The male frog have vocal cords which enable them to make a croaking noise to attract the females during the rainy, breeding season. |
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| The male reproductive system consists of a pair of testis that are attached to the kidneys. Each testis opens into the kidneys with the help of numerous fine ducts called vasa efferentia. Sperms produced by the testis are carried through the ureters and hence, in the male, ureters are called urinogenital ducts. |
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| The female reproductive system consists of a pair of ovaries and a pair of oviducts. Ovaries are attached to the kidneys. They carry numerous ova which are released to outside through the oviducts. |
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| In the breeding season, the male and the female frogs enter into a process of temporary union called amplexus. The male holds the female, presses her trunk and thereby forces the female to release the eggs, in a cluster called spawn. This process is called spawning. The male frog releases sperms simultaneously to bring about external fertilization. |
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| Male Anatomy |
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| Female Anatomy |
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| Development is indirect. It involves the occurrence of a larva called tadpole. It is a small, fish-like creature which hatches out from the egg after completing the development. The tadpole swims freely in water feeding on planktonic food. Initially the tadpoles have external gills which become replaced by internal gills. Limbs appear gradually and tail shortens. Along with these, a few other significant changes take place, transforming the tadpole into a young adult. These changes together constitute metamorphosis. |
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