140 EDUARD UHLENHUTH 
rate of development are doubtless sufficiently great to indicate 
distinctly the differences existing between the Anura and Urodela. 
Under conditions of quantitatively equal feeding (which alone 
ean be taken into consideration in a study of qualitative effects) 
the feeding of thymus to larvae of Amblystoma opacum causes 
accelerated development. 
Nevertheless, the above mentioned experiments become even 
more Clear if the results obtained by them are compared with the 
result in experiments made by a different method; for the fac- 
tor to be emphasized is not the time elapsed since the hatching 
but the size of the animals. The thymus-fed individuals attain 
the stated conditions of development while much smaller in size 
than the worm-fed animals. The latter must attain much greater 
size than the thymus-fed animals, in order to acquire the same 
degree of development. 
In a group of A. punctatum (P. 1916) kept at a high tempera- 
ture, one series was fed with pieces of thymus and another with 
Tubifex. In both series the animals were allowed to eat accord- 
ing to their inclination as a result of which the worm-fed animals 
consumed a considerably larger quantity of food than did the 
thymus-fed animals, and consequently grew much more rapidly. 
The development of the skin pigmentation also proceeded more 
quickly than in the case of the thymus animals, although the 
latter attained these various stages while much smaller in size. 
At the time no exact drawings were made to show the relation- 
ship between the size and stage of development. This will be 
taken up in a recently initiated experimental series of A. puncta- 
tum (P. 1917) as yet incomplete, in which the same system of 
feeding is being maintained as in Group P. 1916. Meanwhile 
it can already be noted that the worm-fed animals do not de- 
velop the yellow network until they have attained the average 
size of 62.91 mm., the minimum length being 59 mm. The 
thymus animals, which have only attained an average length 
of 32.22 mm., with a maximum length of 36 mm., have not yet 
shown signs of this network. In group P. 1916 of A. punctatum 
in which the worm-fed animals behaved like the worm-fed animals 
in Group P 1917 regarding the relation between size and de- 
