Metamorphosis of Amblystoma 
55 
In contrast with Laufberger’s experiments bearing on axolotls 
and to those by Gudernatsch and Romeis on tadpols, thyroi- 
dine feeding had no injurious influence in my experiments. The 
animals treated by these authors did not survive the metamorpho¬ 
sis long; on the photo’s appended to their papers the injurious 
effect of the experiment is quite evident. A judicious dosing of the 
thyroidine-tabloids permitted to induce normal processes of meta¬ 
morphosis; no animal died (except one which was too heavily 
dosed) and some are living in the terrarium even now. after the 
lapse of ten months. 
Details concerning experiments. 
Nine axolotls, blaek and albinotic ones, were fed on thyroidine- 
tabloids (Richter’s make). The size of the animals was from 13 5 
to 20 cm; they lived for more than a year in the laboratory with¬ 
out showing any tendency to metamorphosis. At the beginning of the 
experiment the animal was weighed. Half a tabloid of 025 gr 
thyroidine was given every two or three days; only to one animal 
a dose of 05 gr was given twice; this dose proved too large, the 
animal died after a few da} r s. To avoid starvation, I always gave 
some meat during the experiment After two or three weeks, the 
reduction of gills and fins was evident. The animals were taken 
out of water and put into a terrarium; no more thyroidine was 
given. The resorption of gills and fins was in an advanced stage. 
After moulting the animals showed the appearance of the terrestrial 
form of Amblystoma mexicanum. The appended photo’s are those of two 
metamorphosed animals, nr. 1 of a black, nr. 2 an albinotic one. 
The first striking effect of thyroidine feeding is the increase of 
excrements followed by a considerable diminution of body-weight 
which amounted to 39*8°/ 0 of the initial weight. The loss depended 
upon the quantity of thyroidine given. 
The resorption of the larval respiratory organs begins with the 
reduction of the crest and the fin of the tail. The gills diminish 
slowly .and somewhat later than other organs. In the resorbed or¬ 
gans of albinotic individuals blood-vessels filled with blood were 
observed; this seems to show that deficient circulation cannot be 
considered to have provoked resorption. The webs between the 
toes also diminished gradually; after the first moult the animal 
had no fins at all and only small fragments of gills. 
