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'''Bullfrog '''
Scientific classification

Binomial name
Rana catesbiana
The Bullfrog (Rana catesbiana) is an amphibian, a member of the family Ranidae of true frogs. This frog can be found at lowland near a pond, a lake, or a marshland. They are maily found where the water is quiet and is covered with plants. The diet of a Bullfrog is consist of insects, and larger preys such as small mammals, birds, turtles, snakes, and other anurans. The Bullfrog is native to the USA, but has been introduced to few places in Europe as well. As it forms a risk to the ecosystems there it is now tried to push back its spreading in Europe.

A Bullfrog uses skin, Buccal Cavity, and lungs for respiration. Cutaneose ("skin") gas exchange is very important in all amphibians. Their lung uses a pump mechanism and for the buccopulmonray bentilation is done in three cycles. The first one invloves a raising and lowering of the buccal floor with nares open to allow air into the buccal cavity. During the second cycle the glottis will be opened or closed and the nares would renew the pulmonary air. At the last cycle an apneic pause would interrupt ventilation cycles. This is not a very efficient respiratory mechanism, but it is characteristic of all living amphibians.

The skeleton of an adult frog is consist of 1) bone, 2) hyaline cartilage, and 3) calcified cartilage. The calcified cartilage can be found trough out the body of the frog, its particularly more noticeable in the epiphyses of the long bones in the limbs and shoulder-gridle, etc

The vertebrae of the frog has ten bones, nine are true vertebrae, and the rod -shaped urostyle that is almost as long as the other nine. The head of the frog is flat but its form depends on the extensive separation of the jaw bones; the orbital cavities and the horizontal direction of their floor also have an effect on the form of the head. The central nervous system of the frog is made up of the spinal cord and the brain, where the spinal cord is a bit smaller than the brain. The peripheral nervous system contains the cranial nerves and spinal nerves.

The male reproductive organs are the testes and their duct and the female have their ovaries. In spring at night the male calls the female from the water The female lays up to 10,000 eggs and these eggs will become tadpoles. Their metamorphosis brings them the organs that are only found in the adult frogs and takes between 12-24 months. There are three major changes that take place during the metamorphosis: 1) Premetamorphis which is when the embryo genesis and growth and development occur, during this time the thyroid gland is absent. 2) Prometamorphis is the period in which the concentration of the endogenous thyroid hormone rises 3) Metamorphis is the period when the tadpole's tail will be gone. Other organs too undergo changes such as the liver and the intestine and the gills will be gone as well. The adult frog can live up to 15 years.