Bidder's organ is a spherical, brownish organ in any member of the family Bufonidae, or simply, toads. The organ is located just in front of the kidney, or, mesonephros. It is formed at the cranial tip of the male and female gonad during the larval stage. Normally it is inactive and contains miniature follicles which have the capability to mature (becoming active). Zoologists have experimented with the physiology of the organ by castrating male toads (removing the testes). In doing so, the Bidder's organ enlarges and produces viable oocytes, that is, egg cells, and then it produces gonadotropins, which stimulate the growth of the Müllerian ducts to form uterus and oviducts. It therefore becomes a fully sexually functional female, which leads some zoologists to conclude that toads are actually paedomorphic.
However, the Bidder's organ only develops into an ovary when testes are removed experimentally or not functioning properly (e.g. due to exposure to endocrine disrupting chemicals). Importantly, females can have a Bidder's organs in addition to true ovaries which suggests that the Bidder's organ might not be a rudimentary ovary. The true function of the Bidder's organ remains a mystery.
It is named in honour of Friedrich Bidder.
Read more about Bidder's Organ: Anatomy, Location in A Dissected Toad
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