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AMPHIBIA

AMPHIBIA. Introduction. In earlier times there was a large variety of amphibian life but today only a few groups remain.

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AMPHIBIA

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  1. AMPHIBIA

  2. Introduction • In earlier times there was a large variety of amphibian life but today only a few groups remain. • Of those still in existence, several live in water, and even the terrestrial ones (those which live on land) are partially dependent on water because eggs are only laid in water and even the larvae can develop only in water. • The amphibians are adapted to life both in water and on land. • The only group of amphibians found in South Africa is that which includes the clawed toad and the various types of frog.

  3. Topics of Discussion • THE FROG • HABITAT • BODY SHAPE • BODY COVERING • EXTERNAL STRUCTURE OF A FROG • BODY DIVISIONS • THE HEAD • THE TRUNK • THE LIMBS • THE CLOACA

  4. HABITAT • Frogs live in water. They are aquatic animals. • They prefer pools of stagnant water, dams and slow-flowing streams.

  5. BODY SHAPE • The body is short because the frog has no neck and tail. It has a hump on its back. • The body is slightly flattened from top to bottom.

  6. BODY COVERING • The skin is soft and naked. • Large numbers of mucous glands ensure that the skin is always moist by secreting mucus. • Pigment cells also occur in the skin. These enable the frog to change colour in order to blend into its sorroundings.

  7. EXTERNAL STRUCTURE OF A TOAD

  8. BODY DIVISIONS • The frog is divided into 2 divisions. • These are the head and the trunk but there is no definite division between these regions.

  9. THE HEAD • The head is flat and triangular in shape • It is joined directly to the trunk • It consists of the following parts:-(I)A large mouth which opens widely to take in food. Inside it there is (a) Teeth only in the upper jaw. These are not for chewing but for holding the prey. (b) A large fleshy tongue which is sticky so as to catch the prey. The tongue is attached infront and free at the back, is found on the floor of the mouth. (ii) The two small nostrils are used for smelling and breathing. (iii) The two large bulging eyes enables it to see moving objects. They are covered by a transparent membrane known as the nictating membrane. (iv) The internal ears behind each eye serve as hearing and balancing organs.

  10. THE TRUNK • This forms the greater part of the body. • It is flattened from top to bottom. The following parts are found on the trunk:- • The limbs The forelimbs are short and consist of an upper arm and a forearm that ends in four fingers. The hind limbs are long and muscular. (ii) The cloaca The cloaca is situated at the rear end of the trunk between the hind limbs.

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