Metamorphosis of Axolotls 63 
5. Discussion of results. Conclusions. 
My observations confirmed the observations made by Guder- 
natsch, Romeis and Cottronei that feeding with thyroidine 
accelerates the transformation of amphibians, and LaufbergerV 
observation according to which the same statement applies to axol¬ 
otls which in normal conditions do not undergo metamorphosis at 
all. It has been shown that, by feeding our specimens on adequate 
doses, we are able to elicit processes of transformation analogous 
to those observable under natural conditions, i. e. without injury 
to the organism, and that the transformed axolotls may live. (Four 
Amblystomata lived more than a year and a half in the embryo- 
logico-biological laboratory and died only by accident). 
The question arises, how are thyroidine-feeding and metamor¬ 
phosis inter-connected and whether changes occurring during the 
transformation of axolotls fed on extracts of the thyroid gland are 
identical with those which take place during the normal metamor¬ 
phosis of amphibians. 
The first observable result of feeding on thyroidine is a consid¬ 
erable loss of weight in the animals. Since the resorption of the 
gills and of the fin sets in simultaneously with that loss, we have 
to ascertain whether these phenomena are mutually correlated, whe¬ 
ther the amplification of disassimilatory processes directly causes 
atrophy of the larval respiratory apparatus. 
Such an assumption is supported indeed by the curves repre¬ 
senting diminution *of weight of axolotls fed oh thyroidine. Com¬ 
paring the reduction of the gills and the fin with the form of these 
curves, we see that, where the curve ascends or comes to a sta¬ 
tionary state, the organs undergoing resorption show no conspicuous 
changes whilst, when the curve is descending, they undergo resorp¬ 
tion which takes place the more rapidly as the downward grad¬ 
ient of the curve is greater. Even before the weight-curve began 
to descend, I ascertained changes in the gills; these should be re¬ 
ferred however to injuries to the organism caused by thyroidine, 
injuries which cannot be ascertained by weighing 2 ). The resorption 
q These changes are possibly due to loss of water, ascertained by Schap.er 
and Romeis during natural metamorphosis; Romeis observed that still greater 
loss of water occurs in tadpoles fed on thyroidine. 
