Cell death, thyroxinf and the development of Rana temporaria larvae with special reference to the pronephros

Rana larvae at stages 46–47 (Cambar & Marrot, 1954) in tap water or in 1:5 million concentration of thyroxine (32 days), for almost 3 months at 9°C, are practically unchanged. After 53 days in tapwater at 9°C similar thyroxine-immersed specimens but at 18°–22°C rapidly attain metamorphic climax. During larval development evidence from pronephric development suggests that thyroxine presumably acts by stimulating secondary and dependent mechanisms, which are responsible for the varied morphological and physical changes of the metamorphic cycle.