276 Mary A. Bowers. 



the breaking through of the fore legs. In two individuals, opened 

 at this stage, the reduced intestine was observed to move slowly and 

 steadily, but without visible action of the muscles of the alimentary 

 tube, from its larval position on the left to its adult position on the 

 right. The loop, which had traveled across the body, then made a 

 double coil. 



It is not possible to draw conclusions with certainty from the 

 observation of two cases, but this whole movement appeared to be 

 due to contraction of the mesentery; the intestine seemed to be 

 passive. The mesentery usually contains a large amount of pigment. 

 The fact that aggregations of pigment are often found on the ali- 

 mentary tube after it has passed to the right side of the body, and 

 not before, would seem to add evidence to the view that the contrac- 

 tion of the mesentery is the agent in this movement. 



Bataillon has tested experimentally the question whether the modi- 

 fications of the coil are localized. He curarized tadpoles several 

 days before the appearance of the anterior legs, opened the abdominal 

 cavity and marked equal distances on the small intestine by means 

 of fine pieces of silk thread, which were held in place by the mesen- 

 tery. The cavity was then closed and the animals soon recovered. At 

 the end of metamorphosis examination showed that the modifications 

 are not localized, except that the shortening is slightly more marked 

 at the summit of the coil. 



The cause of the contraction of the intestine may be involved in 

 the puzzling question of metamorphosis, which has never been satis- 

 factorily answered, although many interesting theories have been 

 advanced. 



Reuter suggests that the contraction of the intestinal muscles is 

 perhaps in response to a stimulus derived from the degenerating 

 epithelial cells. In Bufo the first appearance of epithelial degenera- 

 tion and the beginning of the slow muscular contraction are coin- 

 cident, and they may be causally related. Bataillon holds that the 

 changing conditions of respiration and circulation which result in 

 partial asphyxiation, are the causes of metamorphosis. This could 

 hardly be the cause of the contraction, since epithelial degeneration 

 and muscular contraction begin several days before these changes 



