660 



K. RÏCH UND R. WEBER 



SU M MARY 



The induction of metamorphosis has been studied on prometamorphic 

 larvae. Thyroxine ( 1 :5-l : 10 million) was applied by immersion, and the meta- 

 morphic reactions were assessed by means of qualitative criteria. 



From young tadpoles (stage 54 55) viable frogs were obtained. the meta- 

 morphic response decreasing from 24-6 hours of exposure to thyroxine. In tad- 

 poles with thiourea-inhibited thyroids the metamorphic response was greatly 

 reduced at stage 54 55 as compared to normal larvae. but increased progressively 

 from stage 56 57 until the end of prometamorphosis (stage 58/59) with regard to 

 both the number of responding larvae and the degree of metamorphosis. 



Thèse findings demonstrate that in Xenopus larvae there occurs an increase 

 in sensitivity or reactivity to thyroxine during later stages of metamorphosis. 

 They also imply that the progress of climatic events does not require an increasing 

 concentration of thyroxine. 



UTERATUR 



Etkin. W. 1935. The mechanism of anuran metamorphosis I. Thyroxine concentration and 

 the metamorphic paitem. J. Exptl. Zool. 77. pp. 317-340. 



— 1955. Metamorphosis. In " Analysis of Development " (B. H. Willier. P. A. Weiss, 



and V. Hamburger, eds.). pp. 631-663. Saunders. Philadelphia, Penn- 

 sylvania. 



— 1964. Metamorphosis. In " Physiology of the Amphibia" (J. A. Moore. éd.), 



pp. 427-468. Académie Press. New York. 

 Gasche. P. 1944. Beginn and Verlauf der Métamorphose bei Xenopus laevis Daud. Helv. 

 Physiol. Acta 2. pp. 607-626. 



— 1946. Zur Frage des Angriffspunktes des Thiouracils. Experientia 2, pp. 24-26. 

 Geigy. R. 1941. Thyroxineimvirkung auf verschieden weit ennvickelte Froschlarven. Verh. 



Schweiz. Naturforsch. Ges. 121. Jahresvers. Basel. pp. 161-164. 

 Nieuwkoop. P. D. and J. Faber. 1956. Normal Table of Xenopus laevis. North Holland 



Publishing Company. Amsterdam. 

 Ronîeis. B. 1923. Histologische Untersuchungen zur Analyse der Wirkung der Schild- 



drusenfiitterung auf Froschlarven. Roux' Arch. Entwicklungsmech. 



Organ. 98. pp. 579-615. 

 Yamamoto. K.. D. Kanski and E. Frieden. 1966. The uptake and excrétion of thyroxine, 



triiodothyronine and iodide in bullfrog tadpoles after immersion or injection. 



Gen. Comp. Endocrinol. 6, pp. 312-324. 



