38 IOWA STUDIES IN NATURAL HISTORY 
tube in tadpoles of the frog have been described (Ratner 791). 
Data regarding the external changes involved in the metamor- 
phosis of Ambystoma tigrinum are also available (Chauvin ’76, 
Powers ’03). However, a search of the literature reveals no ex- 
tensive quantitative data on the extent of the changes under- 
gone by the digestive tube and other internal organs either in 
an Anuran or an Urodelan species. 
The present paper sets forth the results of quantitative ob- 
servations on the reduction in the length of the digestive tube 
and associated internal changes in correlation with the reduc- 
tion in the total weight of the body, and the coincident period 
of fasting during metamorphosis in Rana pipiens and Amby- 
stoma tigrinum. It also includes a brief consideration of the 
histological changes in the stomach and intestine which are cor- 
related with the reduction in the length of the digestive tube. 
The greater part of this work was carried out at the Iowa 
Lakeside Laboratory during the summer of 1921. The writer 
desires to acknowledge his indebtedness to Prof. R. B. Wylie, 
Director, for the privileges of the Laboratory and for his in- 
terest in furthering the work. 
QUANTITATIVE DATA REGARDING METAMORPHIC 
CHANGES 
The animals used in this study were collected in the vicinity 
of the Laboratory during late July and August. Tadpoles rep- 
resenting various stages of development and young frogs were 
present in abundance. The tadpoles which were still most im- 
mature weighed 3.5 to 4.5 grams and represented a stage of 
development in which the hind limbs were still functionless and 
had attained a length of not over 5 mm. Those which had at- 
tained their maximum larval size weighed 6.5 to 7.5 grams. The 
larvae of Ambystoma also were present in abundance. Those 
used. in this study were relatively small, but quite uniform. 
Those which were least advanced in their development had at- 
tained a length of 9 to 10 cm. and a weight of 5 to 6 grams. 
Those which had attained their maximum larval size were 11.5 
to 12.5 em. in length and weighed approximately 12 grams. 
Larvae which were undergoing metamorphosis were present in 
