EDUARD UHLENHUTH 533 



Relation between Development of Legs and Metamorphosis. 



The statement is usually made that in tadpoles iodine enforces 

 development of the fore limbs and that consequently the limb de- 

 velopment of amphibians is part of the amphibian metamorphosis. 

 We have observed that in salamanders the development of the 

 hmbs, the fore hmbs as well as the hind hmbs, is completely inde- 

 pendent of metamiorphosis; it is not in any way caused or even influ- 

 enced by the iodine mechanism. On the one hand, the legs of thy- 

 mus-fed animals develop at the same rate and to the same degree as 

 in worm-fed control larvae. On the other hand, larvae subjected to 

 iodine treatment do not show any precocious development of their 

 hmbs. In Series Opacum 1917, Wi (described above), the hind 

 limbs had developed only four toes when the larvae were exposed to 

 the iodothyrin solution. Though the iodothyrin, as mentioned 

 above, caused rapid shedding of the skin and reduction of the gills to 

 stubs without fringes, it did not bring about the development of the 

 fifth toe of the hind limbs; thus metamorphosed salamanders resulted 

 with only four toes on the hind limbs. Hence development of the 

 legs is not caused by iodine, but by substances different from those 

 which control metamorphosis. 



In accordance with this, the salamander larvae develop their legs 

 normally if they are deprived of their thyroids even as early as the 

 stage just before the beginning of the blood circulation; for Hoskins 

 and Morris^^ mention that larvae of A?nbysto?na punctatum after thy- 

 roid removal behave like the controls, except that they do not grow 

 so weh; but they do not mention that thyroidectomy prevented the 

 legs from developing. 



From this experiment it is quite evident that in contradistinction 

 to what has been observed in frog tadpoles, in the larvae of the caudate 

 amphibians, leg development and metamorphosis are subject to two 

 different factors, and that, consequently, leg development can occur 

 even if no metamorphosis takes place, or may not occur even if 

 metamorphosis takes place. 



13 Hoskins, E. R., and Morris, M., Proc. Soc. Exp. Biol, and Med., 1916-17, 

 xiv. 74. 



