Tag: introduction to reproduction

Female frogs lay up to 4,000 eggs at a time, which are immediately fertilized by the male. Frogs become sexually mature around four years of age. They emerge from hibernation from February to March to seek out breeding grounds. Females lay their eggs in shallow water. It takes about 40 days for tadpoles to emerge from the eggs.

The truncus arteriosus is formed of a basal thick-walled conus arteriosus and a distal thin-walled ventral aorta. Its conus arteriosus part which is next to the ventricle is known as pylangium and the distal ventral part as synangium. Pylangium is a short tubular structure, while synangium is simply formed by the union of the basal parts of the arteries.

Frogs absorb water through their skin (1), male frogs possess vocal sacs for calling (3), and they have a bilobed tongue for catching prey (5). Hind limbs have five digits, not four, and copulatory pads are on the first digit, not the second.

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 male frogs, sperm travel from the testes via seminiferous tubules, pass through vasa efferentia into the kidney via Bidder's canal, enter the urinogenital duct, and finally exit through the cloaca.

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.