Intestinal Ej)itlioHnni of Bufo Lentiginosus. 267 



the examination of a large number of alcoholic specimens was 

 required before the tadpoles in Figs. 7-10 were found. 



After the appearance of the fore legs and the coincident shortening 

 and narrowing of the intestine, there remains one more marked change 

 before metamorphosis is completed, the absorption of the tail. This 

 shortening usually begins about 48 hours after the fore legs have come 

 through and is completed in from 2 to 4 days. Feeding is resumed 

 on the third or fourth day after metamorphosis is comj)leted. 



MiCEOscopic Changes. 



I. Historical. As stated in the introduction, there have been but 

 three papers on the modification of the intestine of Anura during 

 metamorphosis, — those of Eatner, '91, Renter, '00, and Duesberg, '06. 



Ratner's work does not consider the epithelial changes; it is con- 

 cerned with the subepithelial layers. Renter, using Alytes obstet- 

 ricans, and Duesberg, working with Rana fusca, disagree on the main 

 points of the process. 



Renter recognizes that the epithelium of young larvae is composed 

 of two forms of cells, first, cylindrical, and second, basal round cells, 

 the latter relatively few in number. These "round cells" show fine 

 granular contents and might be mistaken for leucocytes. During de- 

 generation of the epithelium they become more numerous, large and 

 may be multinucleate. They contain great masses, food sub- 

 stance in process of absorption, which are colored brown with Flem- 

 ming. He considers them special absorbing cells. Somewhat later 

 "giant cells" appear, also basal in position and multinucleate, and 

 differing from the "round cells" only in not having the browoi masses 

 and in their fate. Renter claims that both round and giant cells 

 originate by amitosis from the cylindrical epithelium. 



At the beginning of metamorphosis the larvae stop feeding, the 

 round cells receive from the cylindrical cells the last absorbed food, 

 but they do not pass it on into the lymph channels, — they cease secret- 

 ing, become overloaded, die, and with the degenerating cylindrical 

 cells are cast off into the lumen when shortening of the intestine 

 occurs. The giant cells remain, gain the ability to divide rtiitotically , 

 and form the definitive epithelium. 



