Brooding in the stomach
However, the most bizarre form of parental care is the Australian frogs Rheobatrachus silusandRheobatrachus vitellinus. In these species the female frogs swallows the eggs after fertilization and broods them in her stomach for six weeks. Such a breeding system presents interesting problems, such as how the eggs and hatched tadpoles escape being digested within the mother's stomach? The nurturing females appear to cease feeding during the breeding period. The production of hydrochloric acid and pepsin are halted in the stomach by a hormone-like substance prostaglandin E2 which is secreted by the egg capsules and then by the tadpoles. With this shutting down of normal stomach activities, the stomach's digestive functions are transformed into that of a protective gestational sac. The eggs, which range from 21 to 26, are relatively large, ca. 5 mm and rich in yolk. Consequently, the tadpoles do not need an external source of nutrition but feed exclusively on yolk throughout their six-week development period. During birth the female's oesophagus dilates in a manner analogous to the vaginal canal of mammals, and the young froglets are propelled from her mouth. Within a few days after expulsion of the young, the stomach begins to function again as a digestive organ, and the frog resumes feeding. Unfortunately neither of these two species has been found recently, and it is sadly concluded that these interesting frogs are now extinct.