60 
L. Kaufman: 
the mucous membrane is most changed. These investigations prove 
that certain trophic factors may cause results similar to those 
occurring in the intestine of tadpoles during metamorphosis. My 
observations on axolotls undergoing transformation under the 
influence of thyroidine-food may also serve to elucidate the shorten¬ 
ing of the alimentary canal. Feeding with thyroidine amplifies 
disassimilatory processes; this is evident from the loss of weight 
of the animals. We therefore might expect a 'priori that the struc¬ 
ture of the intestines of the axolotls fed on thyroidine would differ 
considerably from the structure of these organs in normally fed 
larvae. As I shall not describe every part of the intestine separat¬ 
ely, I restrict myself to the description of changes occurring during 
metamorphosis in that part of the intestine which adheres to the 
pancreas, i. e. in the duodenum. 
The duodenum of a full-grown normally fed axolotl attains 4 
to 5 mm. in diameter. In a transversal dissection (phot. 5)', we ob¬ 
serve under the microscope one layer of longitudinal and one layer 
of circular muscles, forming a membrane of about 125^ in breadth; 
the submucosa of 20^ in breadth, and the, mucosa which forms 
long (850^) folds. The connective tissue is scantily developed; it 
contains few long cells elongated in the direction of folds. The 
epithelium is composed of high, cylindric cells, of numerous cup- 
cells. In the mucous membrane we remark small blood-vessels, 
sometimes just beneath the epithelium. 
The intestine of an axolotl fed on extract of thyroid gland is 
much narrower than that of a normally fed specimen;, its diameter 
is only 1*5 to 2 mm. Comparing phot. 5 which represents part of 
the transversallv dissected intestine of a normally fed axolotl, with 
phot. 6, representing the analogous dissection of an animal un¬ 
dergoing transformation, we see that in the later specimen the wall 
of the intestine has decreased by more than one half. Only the longi¬ 
tudinal muscles have not undergone visible change; the breadth of the 
circular layer is much smaller than the normal one; it contains more 
nuclei. Owing to these changes the breadth of the muscularis at¬ 
tains only 70 fi. The submucosa which in larvae formed a low 
layer, here attains 100 and it contains numerous nuclei. Consider¬ 
able changes occur in the mucous membrane. In the intestine of 
a normally fed axolotl, the epithelial constituent is considerably 
greater than the connective tissue (phots. 5 and 7); in the in- 
