The Influence of the Hypophysis and the Thyroid on the Ultimobranchial Body of the Anura of Israel

T H E ultimobranchial body of Hyla arborea L., Rana ridibunda Pall., Pelobates syriacus Boettger, and Bufo viridis Laur., the common anurans of Israel, is a paired organ, situated on both sides of the aditus laryngis. Its development runs parallel to the fluctuating activity of the thyroid (Boschwitz, 1960). (a) In the premetamorphic period of relative thyroid dormancy, the ultimobranchial body consists of one follicle with single-layered epithelium in Hyla, Rana, and Bufo, and of a coiled tube with parafollicular cells in Pelobates. A capsule with capillaries surrounds the organ. (b) In the period of metamorphosis up to the beginning of tail-resorption, during which thyroidal activity is heightened, the epithelium of the ultimobranchial body becomes pseudostratified, and the size of the follicle enlarges. In Pelobates the coiled tube changes into several single-layered follicles with parafollicular cells. The whole organ becomes less dispersed. The follicles of all 4 species contain a small amount of faintly eosinophilic coagulum, and often normal-appearing nuclei are embedded therein. (c) In the postmetamorphic period, during which thyroid activity declines, the ultimobranchial body enlarges and differentiates. There is one large follicle with pseudostratified epithelium and shallow folds in Hyla, and one or two large follicles with similar epithelium but deep folds in Rana. There are many small follicles with single-layered epithelium and interspersed clusters of parafollicular cells in Bufo and Pelobates, concentrated in an ovoid organ. The coagulum in the organ of all 4 species is eosinophilic, and includes nuclei, desquamated from the follicular wall. Since the development of the ultimobranchial body parallels thyroid activity in these anurans and its postmetamorphic atrophy in Xenopus laevis may be influenced by the thyroid and the hypophysis (Sterba 1950; Saxen & Toivonen 1955), the influence of the hypophysis and thyroid on the ultimobranchial body has been experimentally investigated and the results are described in the