History Of Frogs

A Frog is a small, tail less animal that has bulging eyes. Almost all frogs have long back legs. The strong hind legs make the frog able to leap farther than the length of its body. Frogs live on every continent except Antarctica, but tropical regions have the greatest number of species. Frogs are classified as amphibians. Most amphibians, including most frogs, spend part of their life as a water animal and part as a land animal. Frogs are related to toads, but are different from them in a few ways. The giant frog of west-central Africa ranks as the largest frog. It measures nearly a foot (30 centimeters) long. The smallest species grow only 1/2 inch (1.3 centimeters) long. Frogs also differ in color. Most kinds are green or brown, but some have colorful markings. Although different species may vary in size or color, almost all frogs have the same basic body structure. They have large hind legs, short front legs, and a flat head and body with no neck. Adult frogs have no tail, though one North American species has a short, tail like structure. Most frogs have a sticky tongue attached to the front part of the mouth. They can rapidly flip out the tongue to capture prey. Frogs have such internal organs as a heart, liver, lungs, and kidneys. Some of the internal organs differ from those of higher animals. A frog’s heart has three chambers instead of four. And although adult frogs breathe by means of lungs, they also breathe through their skin. The eggs of different species vary in size, color, and shape. A jelly like substance covers frog eggs, providing a protective coating. This jelly also differs from species to species. Some species of frogs lay several thousand eggs at a time. But only a few of these eggs develop into adult frogs. Ducks, fish, insects, and other water creatures eat many of the eggs. Even if the eggs hatch, the tadpoles also face the danger of being eaten by larger water animals. The pond or stream in which the eggs were laid sometimes dries up. As a result, the tadpoles die. Certain tropical frogs lay their eggs in rain water that collects among the leaves of plants or in holes in trees. Other tropical species attach their eggs to the underside of leaves that grow over water. When the eggs hatch, the tadpoles fall into the water. Among some species, one of the parents carries the eggs until they hatch. For example, the female of certain South American tree frogs carries the eggs on her back. Among another species of frog, the midwife toad, the male carries the eggs wound around his hind legs. Males of another species, Darwin’s frog, carry the eggs in their vocal pouch. Some tropical frogs lay their eggs on land. They lay them under logs or dead leaves. These frogs have no tadpole stage. A young frog hatches from the egg and begins life as a land animal. Tadpoles are not completely developed when they hatch. At first, the tadpole clings to some support in the water, using its mouth or a tiny sucker. A tadpole has no neck, and so its head and body look like one round form. The animal has a long tail and resembles a little fish. It breathes by means of gills, which are hidden by a covering of skin. A tadpole’s form changes as the animal grows. The tail becomes larger and makes it possible for the animal to swim about to obtain food. Tadpoles eat plants and decaying animal matter. Some tadpoles eat frog eggs and other tadpoles. In time, the tadpole begins to grow legs. The hind legs appear first. Then the lungs begin to develop and the front legs appear. The digestive system changes, enabling the frog that develops to eat live animals. Just before its change into a frog, the tadpole loses its gills. Finally, a tiny frog, still bearing a stump of a tail, comes up from the water. Eventually, the animal absorbs its tail and assumes its adult form. After a frog becomes an adult, it may take a few months to a few