The life cycle of a frog is interesting, because almost all frogs go through 4 distinct phases in their lifetimes. The process begins when a female frog will lay a cluster of gelatinous eggs, either in a water body or on a leaf overhanging one, after which the male frog fertilizes the eggs, only once they have been laid. When these eggs hatch, the emerging creatures look nothing like their parents. A tadpole, or polliwog, has an oval body with a vertically flattened tail. At this point tadpoles are completely aquatic and mostly vegetarian. At the end of the tadpole phase frogs undergo a process called metamorphosis, during which time the tadpole develops very quickly- within a span of 24 hours.
Some of the rapid processes include:
- The disappearance of the gill pouch, making the front legs visible.
- The transformation of the jaws into the big jaws of predatory frogs (most tadpoles are scrapers of algae or are filter feeders).
- The transformation of the digestive system: the long spiral gut of the larva is replaced by the typical short gut of a predator.
- An adaptation of the nervous system for stereoscopic vision, locomotion and feeding.
- Quick growth and movement of the eyes to higher up the skull and the formation of eyelids.
- Formation of skin glands, thickening of the skin and loss of the lateral line system.
- An eardrum is developed to lock the middle ear.
- Once the tail disappears, the frog is ready to leave the water. However, it may take some time after it has begun living on land, for the tail to completely disappear.