Amphibians are cold blooded vertebrates. In the Devonian period of palaeozoic era they were originated from fishes, in the carboniferous period, they increased their number, hence that period is called ‘Age of amphibians’
According to Romer Dipnoi fishes are the “uncles of Amphibians” According to Newman “Dipnoi and amphibians had same grand father.”
General characters of Amphibians
1) Amphibians are cold blooded vertebrates which can hue on land and in water.
2) Amphibians show four limbs with which they can swim in water and jump or walk on the land, (But In apoda limbs are absent.)
3) In Amphibians animals exoskeleton is absent. But in apoda animals small cycloid scales are present.
5)Amphibians Skin is a respiratory organ.
6) The Amphibians skull is dicondylic.
7) Amphibians Ribs are absent.
8)In Amphibians The body divisible into head and trunk Tail is present in, urodela animals.
9)Amphibians Digestive system is well developed. A well developed liver Is present
10) External ear is absent. Middle and inner ears are present, the middle ear columella auris Is present.
11)Amphibians Heart is 3 chambered with 2 auricles and 1 ventricle The blood contains R.B.C. They are nucleated. They contain hemoglobin.
12) Blood vascular system contain hepatic and renal portal systems.
13) Amphibians Kidneys are mesonephric. Urinary bladder is present. It stores urine.
14) Central nervous system is well developed. The brain occupies completely the cranial cavity. The brain is divided into fore, mid and hind brains. Brain continuous as spinal cord.
15)10 pairs of cranial nerves will arise.
16) Sexes are separate.
17) Male and female can be indentified - Sexual dimorphism.
18) In Amphibians the life history a larva stage may be present.
19) Amphibian Eggs are telolecithal, Cleavage is holoblastic unequal.