142 EDUARD UHLENHUTH 
in the 24th week; whereas in the cold worm series no animal 
has yet undergone metamorphosis (in the 32nd week). Thus, 
thymus-fed animals are seen to metamorphose earlier than worm- 
fed animals; that is, provided they receive equal quantities of 
food. 
The relationship of time however becomes inverted if the worm 
and thymus animals, instead of receiving equal quantities of 
food are allowed to eat at will. In a group of A. punctatum 
(P 1916) consisting of two series, which had been kept at a high 
temperature and in which the last-mentioned mode of feeding 
was adopted, the first animal of the thymus series underwent 
metamorphosis after five months, whereas the first of the worm 
series did so after only 35 month 
As in development, so also in metamorphosis, the relationship 
of time is seen to be inconstant and depends on the amount of 
food given to the animals. But a constant factor exists in the 
relationship between size of the animal and metamorphosis. 
Whatever method of feeding may be adopted, the thymus-fed 
individuals are always much smaller when they undergo meta- 
morphosis than are the worm-fed ones. In the Opacum group 
(O 1916) consisting of equally fed animals, the warm thymus 
animals averaged only 47.8 mm. in length at the time that the 
first individual underwent metamorphosis, whereas in the worm 
series at the beginning of metamorphosis the average size was 
53.5mm. The same relationship can be observed at a low tem- 
perature; the average size of the thymus animals being only 57.5 
mm. at the beginning of metamorphosis, whereas the worm 
animals had not yet begun to metamorphose when their average 
length was 65.1 mm. The same conditions apply in the above- 
mentioned Punctatum series (P. 1916); the thymus animals begin 
to metamorphose when their average size is 41.9 mm., but the 
worm animals only at an average size of 50.0 mm. 
As in the case of development, so in metamorphosis the rela- 
tionships obtaining in A. opacum and punctatum are exactly 
the reverse of those found in the Anura larvae, for in the former 
the worm-fed animals must attain a much greater size than the 
thymus-fed individuals before they can undergo metamorphosis 
