448 



J. F. GUDERNATSCH 



It has been shown, however, m the experiments of 1911 that 

 thymus will affect older tadpoles less than younger ones. An- 

 other point may also be mentioned without attempting to explain 

 the situation. Table 6 shows that old thymus-fed tadpoles, when 

 put on a thyroid diet, respond more quickly to the thyroid stimu- 

 lus than do tadpoles of the same age which have been fed on 

 other substances. One should have expected just the contrary, 

 judging especially from Experiment VI in 1911, in which liver- 

 thyroid-fed tadpoles developed their fore legs 3 days earlier than 

 thymus- thyroid-fed ones. 



TABLE 6 



In Experiments II and III those tadpoles (fig. 3 c to h, 3 k, 3 m, 

 3 n ; fig. 4 e to ^, 4 Z, 4 n to p) that were transferred from thymus 

 to thyroid diets were fed on the latter gland only three or four 

 times. When they had developed their fore legs water-plants 

 were placed in the dishes. It had been noticed that thyroid-fed 

 tadpoles would die very soon after putting out fore legs. In these 

 experiments those that were placed in dishes containing plants, 

 although they were never seen to feed on the plants, could be 

 kept alive for some time, 20 to 53 days, while those specimens 

 remaining in water in which thyroid was placed longer than was 

 absolutely necessary for developing the extremities died within 

 10 to 12 days after the beginning of the thyroid diet. Those liv- 

 ing longer did not develop any further than those dying early, 

 but remained stationary except for a further reduction in size, 

 especially of the tail. 



Table 7 gives the length of time that the different thynius- 

 thyroid-fed sets were kept alive in the two experiments. Tad- 

 poles in Experiment III were about 2 days younger than those 

 in Experiment IV, when the feeding began. 



