Metamorphosis of Axolotls 
49 
the only respiratory movements are here the closing and stretching 
of gill-trunks and the gulping of air above the surface, which takes 
place at irregular intervals. 
4. Anatomical and histological investigations. 
I shall not describe all organs nor all changes which occur in 
the anatomical structure of the axolotl during transformation; 
I shall discuss only such details which are of importance for the 
understanding of the connection between phenomena accompanying 
metamorphosis of amphibians. 
The skin. 
It has been shown by Rûziôka that processes of moulting 
which take place in the terrestrial forms of amphibians may be 
considerably accelerated when the animals are subjected to starvation. 
Rûzicka considers accelerated metabolism to be the cause of the 
increased regeneration of the epithelium; for this conclusion he 
relies on the following grounds. During formation of the epithelium 
two processes should be distinguished: regeneration of the epithelium 
in the stratum germinativum and formation of the exuvium. The 
deeper layers of epithelium, situated nearer the blood and lymphatic 
vessels, are better nourished than the superficial layers; the plasma 
of this germinative part undergoes chemical changes by which in 
the surface parts much dead horny substance is stored. This 
impedes the circulation of nourishment to the still more superficial 
layers. By such means at the surface of the skin a dead tissue is 
formed, composed of cuticula and of one layer of stratum corneum; 
during moulting it is cast off. In its place, a new layer appears 
which is formed in the stratum germinativum. The quicker the 
chemical changes occur, the more often the shedding of the horny 
part occurs. The acceleration of moulting in starved amphibians is 
thus a proof of accelerated metabolism. When nourishment is not 
forthcoming, metabolism takes place at the expense of the plasma 
of the germinative layer, which therefore becomes thinner. Such 
is the course of things in full-grown specimens. Why does not 
starvation elicit moult in larvae? according to Rûziëka, because 
the materials which might be used owing to accelerated metabolism 
do not exclusively fall to the share of the skin, but are distributed 
amongst growing organs. If we use older larvae, as was done by 
Bulletin III. B. Janvier—Mars. 4 
