EDUARD UHLENHUTH 



479 



growth in each particular thymus-fed series. We find, then, that in 

 the first three series metamorphosis was greatly retarded (Column 5, 

 Table II). In Series D 1916 metamorphosis should have taken place 

 at 162 days instead of at 207 days, in Series B 1916 at 109 days in- 

 stead of at 133 days, and in Series Tca 1917 at 113 days instead of at 

 122 days. In the other series the retardation of metamorphosis, if 

 there was any at all, was only slight; how far this was due to the 

 special treatment these thymus-fed animals received will not be dis- 

 cussed here. It may be mentioned, however, that in the last series 

 (T 1917) the retardation of metamorphosis was prevented probably 



TABLE II. 



Rate of Growth (R) in Thymus-Fed Amhystoma opacum during Larval Period of 

 Active Growth {Calculated front Averages). 



by adding parathyroid to the thymus diet; since the parathyroids 

 are known to contain small amounts of iodine, it is probable that the 

 thyroid of these larvae was apparently able to store up enough iodine 

 to permit normal thyroid excretion and metamorphosis when the 

 excretor substance began to act. 



The number of days at which the second thymus-fed series (B 

 1916) should have metamorphosed, i.e. at which the excretor substance 

 began to act, is 109. This approaches very closely the time when the 

 drop of the curve occurred (95 days), if we consider that the value 109 

 was calculated only £rom an average value of R X A. 



