38 
L. Kaufman: 
sekretorischen Organen eine Rolle im normalen Embryonal- bzw. 
Larvalleben zuzukommen“. That the thyroid gland plays a part in 
the metamorphosis of amphibians is corroborated by Adler. Tem¬ 
perature variations considerably influence the structure of the 
thyreoidea and the constitution of the colloid contained in its fol¬ 
licles. At the same time the rate of metamorphosis is changed, so we 
may infer that there exists a connection between the structure of 
the thyroid gland and the raetamorphotic processes. 
Gudernatsch’ method has been adapted by Laufberger 
to axolotls. These animals, which in their normal state are neotenic, 
lend themselves especially well to such investigations. Small axol¬ 
otl-larvae (of 6 cm. length) were fed on the thyroid gland of 
oxen and after several days assumed metamorphosed forms. The 
doses were evidently too large 1 ) for young animals, for the trans¬ 
formed Amblystomata lived short time. Writers which studied the 
influence of thyreoidea food on metamorphosis of amphibians do 
not describe physiological and histological changes occurring in the 
organism experimented upon; nor do they express any view as to 
the cause of changes produced by feeding on the thyroid gland; 
they confine themselves to the description of morphological macro- 
scopical changes. 
The question arises whether products of internal secretion regul¬ 
ate also normal metamorphosis of amphibians, i. e. whether the 
hormons formed in the organism act in the same manner as the 
gland given as food. The experiments of Adler may contribute 
to elucidate this question. By means of a galvanocauter he cauterised 
certain glands of internal secretion (the thymus, the epiphysis and 
the hypophysis) and ascertained that alone the removal of the 
hypophysis exerts a notable effect on the course of metamorphosis; 
specimens deprived of this gland do not undergo transformation, 
their growth is supernormal. This influence, however, seems to be 
indirect; histological researches have shown degeneration of the 
thyreoidea. The removal of the hypophysis elicits atrophy of the 
thyroid gland, which in its turn causes retardation of metamorphosis. 
These experiments, as well as those bearing on the influence of 
temperature on the metamorphosis and the connected changes of 
the thyreoidea. indirectly prove that secretion from the thyroid 
1 ) The exact amount of the dose given is not stated in the paper. 
