The excretory system is represented by a pair of primary trunk kidneys.
From the blood passing through the vessels of the kidneys, substances unnecessary to the body are filtered out and urine is formed. From the kidneys through the ureters, urine enters the bladder, and from it enters the cloaca. From a full bladder, urine flows into the cloaca, and then is removed outside.
The excreted end product of nitrogen metabolism in amphibians is urea.
Reproduction and development
Reproduction and development of amphibians occurs in water. The testes and ovaries are paired. Fertilization is most often external. Development with metamorphosis.
Females spawn eggs into water, which are very similar to fish eggs, and males water it with seminal fluid. Sperm cells penetrate the eggs and fertilize them. The shells of eggs in water swell greatly, become transparent, stick to each other, forming lumps, and float to the surface or attach to underwater objects.
After fertilization, the larvae begin to develop rapidly, as a result of which a multicellular embryo is formed in the egg. A few days later, a tadpole larva appears from the egg. The tadpole initially has a tail and resembles fish fry. The tadpole breathes with gills on the sides of the head. He, like fish, has a two-chambered heart and one circle of blood circulation.
In further development, there are lungs, a three-chambered heart, two circles of blood circulation. The hind and front limbs appear, it becomes thinner, shortened, and then the tail completely disappears, and the tadpole turns into a small frog.