Special venous connection between liver and intestine is called hepatic portal system and venus connection between the kidney and the lower parts of the frog is called renal portal system.

Hepatic or gastric caecae are 6-8 narrow and hollow blind tubules called is present at the junction of foregut and midgut. The hepatic caecae are similar to vertebrate liver, secretes digestive juices and help in the digestion.

Frogs are beneficial for mankind because they eat insects and thus, protect our crops. They serve as an important link of food chains and hence food web in the ecosystem, thus maintaining the ecological balance. Some countries use the muscular legs of frog as a food source.

Tissue is the missing in the chain. Structural organisation can be shown as cell-tissue-organ-organ system. Number of cells together form tissue, number of tissue together form organ which on when unit with several organ form organ-system. In organisms like Hydra, the body is comprised of thousands of cells in which each cell works independently whereas in a complex body system as that in humans billions of cells perform various functions together via connecting each other through connecting tissue.