414 HOPKINS. [Vol. XI. 



situated in the fundus of the crypts transformed into gastric 

 cells. 



The differentiation of cells into principal and border cells 

 does not obtain in fishes; whether it occurs in Amphibia is 

 doubtful. Heidenhain and Trinkler (6i) found in the frog 

 only one kind of cell; Edinger, however, found in the frog 

 cells which gave as sharp color differentiation as one usually 

 finds between the principal and border cells in Mammals and 

 Birds. In Necturus maculatus the examination of several 

 specimens by myself failed to show border cells. In an investi- 

 gation on the enteron of Necturus by Dr. B. F. Kingsbury ^ no 

 parietal cells were found. 



The last stage of advance in our knowledge of this subject 

 comprises the period from 1880 to the present time. During 

 this epoch investigations have been directed principally to the 

 determination of the evolution and mode of regeneration of 

 the glandular epithelial cells and to their physiological sig- 

 nificance. 



No one, perhaps, has done more towards the solution of 

 these problems than Dr. Nichola Trinkler. His paper (61), 

 " Ueber den Bau der Magenschleimhaut," is devoted almost 

 exclusively to the consideration of the epithelial cells and their 

 transformations. As the result of various experiments and 

 investigations, he concludes that the parietal cells increase in 

 number during digestion, and that the young cells which arise 

 from them by fission move gradually towards the lumen of the 

 gland, and are there transformed into principal cells, and in 

 this manner serve to replace the destroyed principal cells. 



From experiments with artificial digestion he shows that the 

 parietal cells of higher vertebrates and also the gland cells of 

 lower forms (Frog, Pike) secrete pepsin, but that the presence 

 of the parietal cells accelerates two or threefold the rapidity 

 of digestion of fibrin and egg-albumen. 



Langley (32), in his paper, " On the Histology and Physi- 

 ology of the Pepsin-forming Glands," confined himself princi- 

 pally to the granules of the gland cells and to changes which 



1 The Histological Structure of the Enteron of Necturus maculatus. Proc. 

 Amer. Micro. Soc, Vol. XVI, pp. 18-64, 1894. 



