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

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 ultimo-branchial 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 ultimo-branchial 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 follicl