Vol. XLI. December, 1921. No. 6. 



BIOLOGICAL BULLETIN 



THE EFFECT OF IODINE AND IODOTHYRINE ON THE 

 LARV^: OF SALAMANDERS. II. THE RELATION 

 BETWEEN METAMORPHOSIS AND LIMB DEVELOP- 

 MENT IN SALAMANDER LARVAE. 



E. UHLENHUTH. 

 (From the Laboratories of the Rockefeller Institute for Medical Research.) 



In previous experiments (i) on the larvae of Awbystoma 

 opacum I found that iodothyrine did not accelerate the develop- 

 ment of the limbs, although it caused rapid metamorphosis. Con- 

 sequently, if the administration of iodothyrine was begun at an 

 early larval stage, the metamorphosed salamanders possessed hind 

 limbs which did not have the full number of toes. In agreement 

 with these observations is the fact that feeding of thymus gland, 

 although it resulted in an inhibition of metamorphosis, did not 

 retard the development of the limbs of the thymus-fed salamander 

 larvae (2). Hence it is evident that in salamander larvae the de- 

 velopment of the limbs is independent of the substance (thyroid 

 hormone) which causes metamorphosis. 



The relation between limb development and metamorphosis as 

 it exists in salamander larvae is of especial interest, since < appar- 

 ently it is just the opposite of what should have been expected 

 from the experiments performed on the anuran tadpoles. Through 

 the work of Gudernatsch (3) and many other investigators it is 

 well known that in tadpoles administration of thyroid gland, iodo- 

 thyrine and other thyroid preparations accelerates not only meta- 

 morphosis, but also the development of the limbs. Lately Swingle 

 (4) found that the administration of inorganic iodine which causes 

 precocious metamorphosis of the tadpoles likewise accelerates de- 

 velopment of the limbs. 



307 

 t 



