39 
Metamorphosis of Axolotls 
•gland regulates metamorphosis in the normal evolutive cycle of 
amphibians. No positive conclusions, however, have been arrived 
at as to the connection between internal secretion and metamorphosis 
of amphibians. As for the metamorphosis of insects, a recent paper 
by Kopec proves that the presence of the brain in caterpillars, 
up to a certain period, is indispensable for the inchoation 
of histolytic processes. Kopec considers that the influence of the 
brain on transformation is chemical; to the brain he attributes the 
rôle of a gland with internal secretion. 
Gudernatsch’ discovery that feeding with thyreoidea accel¬ 
erates the metamorphosis of amphibians may possibly elucidate the 
cause of normal transformation in amphibians. For should it turn 
out that all changes in an organism fed on thyroidine are the same 
as those occurring during normal metamorphosis of specimens living 
under usual conditions, we would have to admit that the acting 
cause in both cases is the same. Causal discrimination is easy here, 
because bv feeding with thyroid gland we are able to elicit at will 
•changes leading to metamorphosis. 
It was my object to investigate processes occurring during 
transformation of amphibians fed on thyroidine and the connection 
between feeding on a preparation of thyroid gland and metamor¬ 
phosis. Comparing my results with data referring to analogous 
phenomena which occur during normal metamorphosis, I hoped to 
contribute to the knowledge of the mechanism of regulation connected 
with change of surroundings. 
2. Specimens and methods. 
The axolotls used for these experiments were obtained from 
a zoological agent in Berlin; they li ved for three years in the 
laboratory without showing any tendency to metamorphosis, even 
in shallow water. I endeavoured to elicit changes similar to those 
observable under natural conditions, i. e. without injury to the 
organism. x4uthors which investigated the effect of thyroidine food 
on the metamorphosis of amphibians fed their specimens exclusively 
on thyroid gland. But proceeding in this way we superimpose, upon 
the effect of thyroidine, the influence of starvation all the more 
«effectual since the extract of thyreoidea causes rapid metabolism. 
I fed therefore my animals on meat also which I gave together 
with thyroidine or alternatively. Thyroidine was given in tabloids 
