35 
Metamorphosis of Axolotls 
died from asphyxia or from exhaustion before having completed 
metamorphosis, it may be concluded that the conditions in which 
they lived were pernicious and paralysed vital processes. Never¬ 
theless, for the examination of the course of transformation such 
experiments are of value which show the influence of certain fac¬ 
tors on the duration of the larval stage and the function connected 
therewith, without implying any injury to other normal functions. 
In other experiments, Wintrebert transferred the tadpoles of 
Rana esculenta from water on wet moss in a closed tube. Under 
these conditions, the animals underwent metamorphosis sooner than 
usually. From these experiments we may also conclude that the 
impossibility of breathing oxygen accelerates metamorphosis: the 
interchange of gases in these animals is rendered difficult for 
a certain time (before air-breathing is definitely evolved). Win¬ 
trebert put axolotl-larvae, of 10 cm. length, into an aquarium, 
so that only a part of the animal's body was covered with water. 
The larvae underwent metamorphosis when the aquarium was open; 
in an aquarium covered with glass, the animals went on land but 
in moist air they did not metamorphose and, when transferred into 
water, resumed former appearance, i. e. the reduced gills and fins 
regenerated. This observation shows that for certain organisms even 
small amounts of water suffice for interchange of gases by means 
of gills; the complete removal of the function of the gills causes 
the processes of metamorphosis. 
Besides these external factors, various authors also mention tem¬ 
perature as regulating the duration of larval life. This influence 
was studied by Adler. An optimum of temperature exists for 
the metamorphosis of amphibians; at higher temperatures, growth 
as well as transformation undergo retardation. As the retardation of 
metamorphotic processes prevails, the transformed frogs are some¬ 
what larger than those used as standard. The same behaviour is 
observed in cultures subjected at first to the influence of high and 
then to that of low temperatures. Tadpoles which were cultivated 
at low and then at high temperatures are also delayed in their 
growth and metamorphosis, but as the retardation of growth accu¬ 
mulates, transformed animals are smaller than normal. Barfurth 
and Kämmerer ascertained that low temperatures cause retard¬ 
ation; high temperatures (but not higher than the optimum) acceler¬ 
ate metamorphosis. 
3 * 
