Leg development in a frog without a tadpole (Eleutherodactylus coqui).
Direct developing frogs, like Eleutherodactylus coqui, have deleted the tadpole from their life history. Limb buds appear early and develop continuously through embryonic life. The capacity for autonomous development of E. coqui limb buds was tested by explanation and transplantation. When limb buds were explanted to in vitro culture, they progressed for a few stages and then arrested. When limb buds were transplanted to embryos of a typical tadpole species (Rana pipiens), the buds formed legs with knees, digits, and some cartilage, but they did not elongate. Since limb buds transplanted to various sites on E. coqui embryos tended to develop completely, the limited development of the explants in vitro and the transplants to R. pipiens suggests the presence of a systemic factor in the embryo involved in the normal continuous growth of E. coqui legs. Attempts to demonstrate a role for thyroid hormone have thus far been unsuccessful.