INFLUENCE OF THYMUS FEEDING UPON DEVELOPMENT 145 
the last (leaving two animals out of consideration) after 63 
months. In the case of these thymus-fed animals the period 
of metamorphosis lasted 2 months, for instance, not longer than 
in the case of the worm animals; but 2 of these thymus animals 
not yet mentioned, behaved very differently from all the other 
animals. They both remained at a low stage of development, 
so far as coloring was concerned, and their tails underwent but 
slight reduction in size. On the other hand, the gills were re- 
duced to short stumps. Although neither of these 2 animals 
was shedding its skin (which should take place befere meta- 
morphosis) at the time of the reduction of the gills, they were 
taken out of the water and placed in a vessel, the bottom of 
which was covered with filter paper and just enough water to 
keep the vessel wet. But neither of the animals showed any 
further change, until finally 123 months after hatching one of 
them shed its skin and its gills became completely atrophied, 
while at the same time the skin became darker in color although 
the yellow network failed to develop. The other animal is still 
in the larval stage, 132 months after hatching. 
We must not fail however to mention that it still appears very 
doubtful whether this is a direct effect of thymus, for a similar 
phenomenon was also noted in the case of worm-fed animals, 
although not to so extreme a degree. Out of approximately 
300 worm-fed animals, only 1 individual showed such a condition; 
after more than 8 months it was still in a larval condition and 
had not developed a trace of the yellow network. The fin of 
its tail was but slightly reduced; its gills were more reduced 
and the animal was still undergoing growth and taking food 
spontaneously. It was used for the purpose of an operation, in 
the course of which it died. However, as has been said, at this 
stage it showed no trace of approaching metamorphosis. From 
this it seems very doubtful that the delay of metamorphosis 
in the two last mentioned thymus animals was actualky due to 
the action of thymus and we must exclude them from discussion 
until the same phenomenon is obtained in a greater number of 
cases. 
TAE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 23, No.1 
