150 EDUARD UHLENHUTH 
this step. During this week the curve of the body size of the 
cold thymus animals, which up to that time occupied the second 
position, can be seen to cross that of the warm thymus animals. 
From the time that the first animal of the warm thymus series 
entered upon metamorphosis, the warm thymus animals com- 
pletely stopped growing. ‘Their curve, which of course does not 
include the metamorphosed animals, is soon after crossed by 
those of the two series of worm animals, and the warm thymus 
animals remain smallest in size for the rest of the experiment. 
The cold thymus series, the first individuals of which under- 
went metamorphosis in the 24th week, also increase in size only 
a little from the time of metamorphosis on; but as the first 
animals of the warm worm series which is most proximate to 
the cold thymus curve similarly undergo metamorphosis in the 
24th week, and also because the curve of the cold thymus animals 
is higher above that of the warm worm animals than the curve 
of the warm thymus animals is above the cold thymus animals, 
the curve of the latter remains the first at the beginning; it is 
not crossed by that of the warm worm animals until the latter 
have all metamorphosed. Finally, in the 29th week, together 
with the curve of the warm worm-fed animals, it is crossed by 
the curve of the cold worm series, which now occupies the first 
position. As early as the end of the 29th week the largest animals 
of the cold worm series have attained a size greater than that of 
each non-metamorphosed (and of course of each metamorphosed) 
individual of the three remaining series. As for the present 
(after the 32nd week) the animals give no sign of impending 
metamorphosis and continue to grow. 
The above-reported circumstance appears to us to be the 
most instructive with reference to the statement that thymus- 
fed anuran larvae attain a size by many denoted as abnormally 
large but stated by Romeis never to exeeed normal limits, al- 
though sometimes exceeding the size of the muscle-fed animals. 
If we begin by comparing each of the two thymus series with the 
corresponding worm series, we see that the same relation exists 
between them as between muscle and thymus-fed tadpoles, inas- 
much as the animals which metamorphose later attain greater 
