37 
Metamorphosis of Axolotls 
this into consideration, we see that Batai lion’s „theory of 
asphyxia“ (even if true) would only concern Anura in which the 
appearance of fore-limbs directly precedes the resorption of respir¬ 
atory organs. 
A new direction was given to the study of the transformation 
of amphibians as soon as the problem of internal secretion gained 
in general interest. In 1905 Babâk cut off parts of the central 
nervous system in tadpoles and observed that specimens deprived 
of the hind parts of the brain did not undergo metamorphosis, if 
the operation was made before the appearance of the fore limbs. 
On this ground he believes that parts of the brain may influence 
metamorphosis indirectly, chemically, owing to the connection exist¬ 
ing between circulation, respiration and the nervous system. Fur¬ 
ther investigations on glands with internal secretion have shown 
that the metamorphosis of amphibians is influenced by chemical 
factors; but hormons are secreted here, not by parts of the brain, 
but by the thyreoidea and the thymus. From. Gudernatsch 5 
experiments it follows that feeding with thyroid gland causes quick 
differentiation but retardation of growth; the effect of feeding with 
thymus, on the other hand, is stagnating differentiation and accel¬ 
erating growth. Gudernatsch fed larvae of frogs (Pana tempo- 
raria and esculenta) on thyroid gland of oxen and observed trans¬ 
formation, more early than usual, into dwarfed frogs which he 
keeped alive for weeks. The same result was obtained by Cot- 
ronei in tadpoles of the edible frog and of the toad, fed on the 
thyroid of dogs. Romeis made similar experiments; he analysed 
the substances contained in tadpoles normally fed and in those fed 
on thyroidine-tabloids. He thus found that specimens fed on thyr- 
oidine become thinner owing to loss of organic and mineral sub¬ 
stances. The diminution of weight is much larger than during nor¬ 
mal metamorphosis, it depends upon the quantity of thyroidine 
given. When small doses are given, it is possible to bring up 
dwarfed frogs able to live for some time. Too large doses cause 
death from exhaustion, as thyroidine influences processes of meta¬ 
bolism. From these observations, Romeis draws the following 
conclusion: „Die vorliegenden Untersuchungen und die darauf ge¬ 
gründeten theoretischen Überlegungen legen den Gedanken nahe, 
daß zwischen Neotenie und innersekretorischen Organen korrelative 
Beziehungen bestehen können. Ferner scheint gewissen inner- 
