Thyroid growth and its relationship to metamorphosis in Rana temporaria.

INTRODUCTION In a previous work on pronephric degeneration, larvae of Rana temporaria from practically the whole range of the metamorphic cycle were studied (Fox, 1962). Metamorphosis in anurans is dependent upon the presence of a functional thyroid gland (Kollros, 1951; Lynn & Wachowski, 1951; Etkin, 1964), and the same specimens have now been used to investigate thyroid growth and development quantitatively and qualitatively, especially in relation to those major events which occur at the metamorphic climax between stages 49 and 54 (Cambar & Marrot, 1954). It will be shown that in larvae from 16 mm long (stage 41; see Fox, 1962) until practically the end of the climax (stage > 53), thyroid cells are of stable volume (about 700 /A), and thyroid enlargement is by cellular proliferation and vesicular expansion. The maximum rate of thyroid growth occurs between 16 mm and 28 mm (stages 41-45).