METAMORPHIC CHANGES, R. PIPIENS 41 
in the larvae of Rana pipiens reach their highest point at ap- 
proximately the same time. The curve representing the total 
weight of the animals reaches its highest point a little later. Ob- 
viously, the larvae cease to feed before resorption of the tail 
is initiated. The period of fasting continues until the meta- 
morphie changes are complete and the little frogs have emerg- 
ed from the water. When the larvae cease feeding the stom- 
ach and intestine are well filled. The ingested material, there- 
fore, accounts for the greater part of the total weight of 
these organs with their contents when the curve reaches the 
highest point. As the metamorphic changes advance the con- 
tents of the digestive tube are gradually eliminated until the 
residue left in the large intestine becomes almost negligible. 
Therefore, the lowest point in the curve represents approximate- 
ly the weight of the stomach and the intestine without contents. 
Many of the little frogs which were collected in the grass 
after they had emerged from the water were still without 
food in their stomachs. Obviously, feeding is not resumed 
until at least a short time after the little frogs emerge. Larvae 
which had attained their maximum size when they were 
brought into the laboratory, and in which resorption of the tail 
was initiated soon after, were completely metamorphosed nine 
to ten days later. Therefore, it may be assumed that the per- 
iod of fasting is of at least ten days’ duration. This is prob- 
ably a fairly accurate estimate of the interval required for the 
completion of the metamorphic changes in this species. It cor- 
respends closely with the interval required by the metamorphic 
changes in R. fusca as determined by Schaper’s observations on 
larvae which were reared in the laboratory. 
The liver does not reach its maximum weight until the resorp- 
tion of the tail and the digestive tube are well advanced. It 
then decreases rapidly until it reaches the minimum weight 
about the time metamorphosis is completed. 
Curve A’B’, fig. 1, illustrates the changes in the total weight 
of the larvae of Ambystoma tigrinum as they approach and 
pass through the period of their metamorphosis. This curve 
shows a rapid rise until its highest point is reached; then an 
abrupt decline. It indicates a reduction in weight from an 
average maximum of 12.2 to an average minimum of 8.7 grams, 
