46 IOWA STUDIES IN NATURAL HISTORY 
has been denied by certain observers (Valatour; P. Schultze). 
On the other hand, Ratner states that few longitudinal muscle 
fibers are present even during the earlier metamorphic changes. 
The present study warrants the conclusion that longitu- 
dinal muscle fibers are present in the muscularis of the stom- 
ach during metamorphosis. The submucous connective tissue 
also becomes more abundant and the gastric glands become ar- 
ranged more compactly. An advanced stage in the progress 
of these changes is illustrated microphotographiecally in figure 
4, which is taken from a transverse section of the stomach of 
a tadpole in which this organ had almost reached its maximum 
size during metamorphosis. Figure 5 illustrates microphoto- 
graphically a portion of a transverse section of the stomach of 
a tadpole in which the growth of this organ after reduction was 
initiated. All the layers except the mucosa are relatively 
thicker than in the preceding stage. The muscularis is now 
represented by a thick layer of compactly arranged fibers. The 
submucosa consists of a well defined layer of connective tissue 
between the muscularis and the deep portions of the gastric 
glands. The latter are short and more compactly arranged 
than in the preceding stages. Figure 6 illustrates micropho- 
tographically a portion of a transverse section of the stomach 
of a young frog recently emerged from the water. The mus- 
cularis is not proportionately thicker than in the preceding stage. 
The submucosa is somewhat thicker and more fibrous. The gas- 
tric glands are quite fully developed. In short, the stomach 
now shows the histological structure of the stomach of the adult 
frog. 
The small intestine of the frog tadpole is arranged in a char- 
acteristic double spiral coil which, while the tadpole is growing 
and actively feeding, causes marked distension of the abdomen. 
As the tadpole undergoes metamorphosis and the intestine be- 
comes shorter, the spiral coil becomes smaller and finally gives 
way to the arrangement of the small intestine in the adult 
frog. Several stages in the reduction of the intestinal coil are 
illustrated photographically in figure 7. Until the process of 
shortening sets in, the wall of the intestine is extremely thin 
and fragile. It consists of little more than the thin serous and 
muscular layers and the mucous epithelium which, while the 
