EDUARD UHLENHUTH 



309 



It is quite different with the prevention of metamorphosis by the 

 thymus. If normal food is added to the thymus diet, metamorphosis 

 will take place in each individual at the same time as in the controls. 

 This is shown in the following experiments on larvae of Amby stoma 

 maculatum of the same age, from eggs of the same female, and all 

 kept at approximately 25°C. One series of 30 larvag was fed only on 

 worms, one series of 15 larvae only on thymus, and one series on 

 thymus and worms alternately. Fig. 1 shows the result. The larvae 



Fig. 1. Effect of worm diet when added to thymus diet upon metamorphosis 

 and tetany in Amhy stoma maculatum larvae. Curves indicate percentage of 

 tetanic animals. 



of the mixed food series metamorphosed simultaneously with those 

 of the control series, which were fed on worms only; while in the 

 series fed on thymus, metamorphosis started when all animals of 

 the series fed on worms and on worms and thymus alternately had 

 already metamorphosed, and the last larval animal died about 12 

 weeks later without having metamorphosed at all. In other words, 

 in the series fed on mixed diet the food added to the thymus diet con- 

 tained the substance which is necessary for metamorphosis and which 

 is lacking in the thymus ; and thus this substance was introduced into 



