Tag: zoology

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. 

In frog growth and metamorphosis are controlled by hormones synthesized by endocrine glands near the front of the body. Neurosecretory cells in an insect's brain secrete a hormone, the prothoracicotropic hormone that activates prothoracic glands, which secrete a second hormone, usually ecdysone, that induces ecdysis. PTTH also stimulates the corpora allata, a retrocerebral organ, to produce a juvenile hormone, which prevents the development of adult characteristics during ecdysis.

The frog egg is surrounded by an albuminous layer by an oviduct which later it comes into a uterus. The oviduct is a long coiled duct with the thick wall that is not connected with kidneys.  It consists some glands which secrete albumen that hardens ova. After the ovulation, the cilia of the oviducal funnel draws the coelomic fluid with ova which moves into the middle region with the help of cilia.