Second, in the process of growing up, two hind legs will gradually appear and the tail will gradually become shorter.
Third, the two front legs will grow out and the volume will gradually increase.
Finally, the tail disappeared completely, and then it evolved into a frog.
Specific process
1. The newly hatched tadpoles are spindle-shaped, with no limbs, mouth and inner gills, long tail, flat side and branched outer gills on both sides of the head, which are adsorbed on aquatic plants and fed by the remaining yolk in the body.
2. After a few days, a mouth grows, which can eat microorganisms in the water. After a period of time, the outer gills disappear, the inner gills grow, the lateral lines gradually appear outside the body, and the heart develops into atria and ventricles, which look like a fish from the external shape to the internal structure.
After about 3.40 days, tadpoles began to grow hind limbs first, and then forelimbs. The tail gradually becomes shorter; The inner gill disappeared and the lung formed; The heart changes from one atrium and one ventricle to two atria and two ventricles; The external morphology and internal structure are no longer like fish, and tadpoles have become young frogs.
4. Young frogs come out of the water and gradually develop into adult frogs.
Tadpole (tadpole in English), written as "Kedou" in ancient times, is the larva of frogs and toads, also called toad ball. The newly hatched tadpoles are spindle-shaped, with no limbs, mouth and inner gills, long tail, flat side and branched outer gills on both sides of the head, which are adsorbed on aquatic plants and fed by the remaining yolk in the body. Mainly in groups. When tadpoles mature, they begin to lose their shape, gradually grow limbs, and then (for frogs and toads) gradually degenerate their tails through apoptosis (controlling cell death).