1. Sea water becomes more saltier as the time passes. Initially, sea water was less saltier and blood of the fishes was at equillibrium. However when the salt concentration of the sea increased, the fishes needed a mechanism to regulate the salt concentration in the blood. Because if the salt concentration of sea is more than that of the blood, water in blood will go to sea by osmosis and the fish will die of dryness. To overcome this problem, fishes have developed hypoosmotic regulators.
2. Caudates have internal fertilization in which packets of sperm is deposited in a gelatinous coating known as spematophore by males known as spematophore and those are uptaken by the females.
Anurans have external fertilization in which the sperm and the eggs are laid in the water where the fertilization occurs.
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