56 L. Kaufman: Metamorphosis of Amblystoma 
The skin of the black axolotl which in the larval state is of 
a dark olive-green complexion, with indistinct yellowish spots ; be¬ 
comes in the metamorphosed Amblystoma quite black with pale 
yellow spots; these appear one after the other. 
Another feature of the metamorphosed animal are prominent, 
convex eyes (cf. both photo’s). 
Among the physiological characters of the Amblystoma , the mode 
of respiration must be mentioned: after a few minutes of terrestrial 
life, the terrestrial form exhibits movements of the throat which 
were not observed in the larvae. 
The anatomical and histological structure of the lungs is the 
same in both forms, in the larval and metamorphosed one; they 
are well developed, large organs. 
The structure of the skin of the Amblystoma differs essentially 
from that of the larval stage; it will be described in the definit¬ 
ive paper. 
Connected with the preceding observations are some interesting 
problems. The first is, what are the physiological changes, due to 
thyroidine feeding, by which metamorphosis is induced. One of the 
most evident effects of feeding with extracts of thyroid gland is 
a considerable diminution of the animal’s weight; it may therefore 
be supposed that rapid metabolism and the digestion of the amphi¬ 
bian’s own albumen produce the resorption of gills and fins and 
are thus the primary cause of metamorphosis; it would be satisfact¬ 
ory to know, however, that other inanition factors can also effect 
the transformation of axolotls. 
Another problem relates to the function of the thyroid gland 
in the organism during metamorphosis. As yet I have not been able 
to find this gland in my animals; it may perhaps be feebly devel¬ 
oped in the axolotl, in the extensive literature, indeed, referring 
to the glands of internal secretion I have found no mention of the 
thyroid of Amblystoma. I may possibly succeed in finding the gland 
in microscopical dissections through the animal’s throat. 
Ernbryologico-Biological Laboratory, University of Cracow. 
