Tag: frog

The egg of the frog is mesolecithal as moderate amount of yolk is present. As the yolk is concentrated in the lower part of the egg and the cytoplasm in the upper part, these eggs are moderately telolecithal. 

In the frog, each kidney is composed of several structural and functional units called uriniferous tubule or nephrons. Two ureters emerge from the kidneys in the male frogs. The ureters act as a urinogenital duct which opens into the cloaca. The thin-walled urinary bladder is present ventral to the rectum which opens in the cloaca.

In the male frog, the final digestion takes place in the intestine. Digested food is absorbed by the numerous finger-like folds in the inner wall of the intestine called villi and microvilli. The undigested solid waste moves into the rectum and passes out through cloaca. Hence the urinogenital duct of the male frog opens into the cloaca.

Fertilization in frog is external. The female releases her eggs from her body into water. Then, the male releases his sperm to fertilize them.

In frogs, the vitellin membrane and an adhesive jelly coating, also known as tertiary egg membrane, surround the eggs. When passing from the oviduct, it is added to the egg. This jelly enables the egg to be easily trained. The capable sperm readily fertilizes the egg as it has the location of the jelly receptor. The frog egg on the animal pole has yolk on the vegetable pole and nucleus.

The female frog secretes jelly like substance that covers the egg. This coating is an oviducal secretion, that is secretion of the oviduct, that helps the eggs clump together, stay afloat and prevent being eaten away by predators.

In almost all frogs, egg fertilization happens outside the female's body instead of inside. The female releases her eggs and the male releases his sperm at the same time. In order to make sure that the sperm reach the eggs, the male and female get into a mating posture called amplexus. The male climbs onto the female's back and clasps his forelegs around her middle.