■prv'-. . 
Metamorphosis of Axolotls 71 
2. After several thyroidine doses, metamorphosis proceeds spon¬ 
taneously, although the animals are left in water. 
3. Extract of thyroidea causes considerable loss of weight, even 
in axolotls abundantly fed on meat. This depends upon the quant¬ 
ity of thyroidine given in food; it sets in several days after the 
beginning of the experiment. 
4. Simultaneously with the emaciation of the axolotls, the re¬ 
sorption of their gills and fin begins; its rapidity is in proportion 
with the previous loss of weight. 
5. Histological investigation of, organs of axolotls fed on thyr¬ 
oidine proves that that feeding accelerates metabolism; its influence 
is similar to. but more intense than, long starvation. 
6. The lungs are equally developed in the larva and in the 
terrestrial form. 
7. Feeding with thyroidine delays the development of the sex¬ 
ual glands. 
8. The thyroid gland, in larvae as well as in terrestrial forms, 
is composed of two small vesicular bodies situated symmetrically 
on the sternohyoideus muscle, close to the caudal part of the genio- 
hyoideus muscle. Sometimes a third thyreoidea may be observed, 
situated in. the middle line between the two geniohyoidei. 
9. The thyroid gland of the larva is composed of small vesic¬ 
les, having a high epithelium which forms intra- and intervesicular 
outgrowths. Colloid cannot be found in all vesicles. 
10. The thyroid gland of transformed specimens contains much 
larger vesicles with a very fiat epithelium. No epithelial outgrowths 
are present. The colloid is strongly coloured by eosine, it fills up 
all the vesicles. 
11. Metamorphose processes may be caused by various chem¬ 
ical factors accelerating metabolism, e. g. by feeding axolotls on 
meat with salicylic acid. 
12. During the natural transformation of amphibians, a factor 
intervenes whose influence is the same as that of thyroidine given 
as food. 
13. All changes occurring during metamorphosis are identical 
in normally fed animals and in axolotls fed on adequate doses of 
thyroidine. 
14. All known data referring to the influence of external fac¬ 
tors on the course of metamorphosis of amphibians agree with the 
V 
