16 E. R. HOSKINS AND M. M. HOSKINS 



larva might have grown still more. Only one hind leg showed 

 any sign of regeneration, and it grew to only half the size of the 

 one removed. When this regenerated leg was removed the 

 animal was unable to regenerate it again. 



The steadily increasing amount of time required to regenerate 

 the removed caudal tissues and the failure in regeneration of 

 removed legs indicates that, although thyroidless larvae are able 

 to grow and regenerate tissues more than a year after the ex- 

 tirpation of the thyroid, the larva will not continue to regener- 

 ate removed tissues indefinitely or at the same rate as the first 

 regeneration it produces. Allen ('18) has noted that young 

 thyroidless larvae are able to regenerate removed parts of the 

 body. Zeleny ('09) found that in normal Salamander larvae 

 repeated amputation of the tail causes an increase in the rate 

 of regeneration. This is influenced, however, by additional in- 

 juries to the body, such as removal of one or both hind legs. 

 If the additional injuries are severe, a decrease in the rate of 

 regeneration is to be observed. 



Forced metamorphosis. An attempt was made to force a thy- 

 roidless larvae into metamorphosis. The total length of the 

 animal was 59 mm.; the nose-anus length, 24 mm.; the length 

 from the nose to the end of the body cavity, 20 mm.; that of 

 the hind legs, 4.5 mm., and the volume was 1.90 cc. This larva 

 was placed in a moist chamber on a bed of wet spirogjn-a, where 

 it lived for two days. It is probable that with care animals 

 might be kept alive in such conditions much longer. This speci- 

 men breathed at irregular intervals. In the forty-eight hours 

 during which it hved in the moist chamber, its tail shrank 24 

 per cent, its anal canal about 50 per cent in volume (due mostly 

 to discharge of contents), and its volume decreased 18 per cent. 

 The gut shortened little, if any, but was strongly contracted. 

 The lungs were filled with air. The shrinkage was not due to 

 inanition, for if a larva similar to the one described is kept in 

 water without food it will maintain its volume for a much longer 

 period than that given to the experiment. Moreover, the shrink- 

 age which finally results from inanition is uniform, while in this 

 experiment the tail shrank first of all, and very rapidly, as it does 



