40 



Messrs. J. S. Huxley and L. T. Hogben. 



prominent. All four, however, died between the fourth and fifth weeks of 

 the thyroid diet, when practically metamorphosed. It was not possible to 

 say whether death was due to internal causes resulting from a too-precocious 

 transformation, or whether it was due to the animals not being able to 

 climb out of the water : that this latter suggestion might well be valid is 

 shown by the fact that the animals' legs at this stage were proportionately 

 smaller, and especially slenderer, than at later stages, and were quite 

 possibly too weak to support the creatures on land. On the other hand, 

 other Amblystoma, transformed by thyroid, usually remained several days in 

 water after completion of all. visible morphological metamorphic changes ; so 

 that death is most probably to be ascribed to internal changes, especially since 

 it is known that in Anura there is a lower limit of size below which thyroid 

 diet induces an attempt at metamorphosis, but one which is always followed 

 by death. 



A single larva was next put on thyroid diet on August 16, 1920, i.e., when 

 about 4 months old and 59 mm. in length. The animal showed meta- 

 morphic changes after 15 days, came out of the water after 26 days, and lost 

 the last traces of gills after 29 days. Metamorphosis can thus be induced in 

 Amblystoma that have not yet attained a length of 2£ inches ; it is possible 

 from then onwards at any size or age. Three more larvae were started on the 

 thyroid diet on August 9, 1920, when nearly 5 months old. The first 

 traces of change were observed on the 17th day, the gill-filaments were all 

 resorbed by the 23rd day, and all emerged from the water between the 30th 

 and 32nd days. A slight diminution in size had taken place in the process, 

 the original lengths of 68, 60, and 60 mm. being reduced to 64, 59, and 

 58 mm. respectively. 



The following experiment was carried out to see whether immersion in 

 dilute alcohol would accelerate or retard the metamorphosis caused by 

 thyroid. Five dishes were prepared, one with larva in each. All contained 

 600 c.c. of liquid. (P) contained water, and the individual in it was fed on 

 meat as a control. (T) also contained water, but the animal in it was fed on 

 thyroid. (Q) contained 1/3 per cent, alcohol, (E) 1/6 per cent, alcohol, and 

 (S) 1/12 per cent, alcohol. The animals in (Q), (E) and (S) were all fed on 

 thyroid. The alcohol solutions were changed thrice weekly. The experiment 

 was started on November 5, 1920. It was very noticeable that the animals 

 in the alcohol solutions were, especially at first, more sluggish than either of 

 those in plain water. They did not at first react to stimulation, but, after 

 the stimulus had continued for some time, they responded by abnormally 

 violent movements. After 2 to 3 weeks, however, they apparently became 

 acclimatised to the alcohol, for their sluggishness was not nearly so marked. 



