METAMORPHIC CHANGES IN THE 
DIGESTIVE SYSTEM IN RANA PIPIENS AND 
AMBYSTOMA TIGRINUM 
By ALBERT KUNTZ 
St. Louis University School of Medicine 
INTRODUCTION 
The changes involved in the metamorphosis of the frog are in 
general well known. The resorption of the tadpole’s tail, the 
gradual elongation of the hind limbs, the emergence of the fore 
limbs, and the initiation of pulmonary respiration are familiar 
phenomena. Less conspicuous, though quite as important, are 
the changes which take place in the digestive tube as the young 
animal, which during its larval life was essentially herbivorous, 
becomes prepared for a carnivorous diet. These and other in- 
ternal changes, and the period of fasting which is coincident 
with them, also involve material reduction in the size and weight 
of the body. 
Metamorphic changes are less extensive in the Urodela than 
in the Anura. However, the more important changes which oc- 
cur in the two orders are similar in character. The resorption 
of the fin-folds and the gills and the initiation of pulmonary 
respiration in the Urodela are accompanied by important 
changes in the digestive tube (although the larvae are not her- 
bivorous) and other internal organs which, with the coincident 
period of fasting, result in a reduction in the size and weight 
of the body which is only less marked than in the Anura. 
Data regarding the function of the leucocytes in the resorp- 
tion of tissue and the histological changes involved (Barfurth 
87, Griffiths 794, Noetzel 95), as well as quantitative observa- 
tions on the rate and extent of reduction in the size and weight 
of the body of the tadpole of the frog during metamorphosis 
(Schaper ’02), are available. The more important histological 
changes involved in the reduction in the length of the digestive 
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