No. 3-] OESOPHAGEAL GLANDS OF URODELA. 103 



function at the expense of the oxyntic function, and the 

 posterior the oxyntic at the expense of the zymogenic function, 

 thus foreshadowing in a parallel way the histological differ- 

 entiation which is seen in the chief and parietal cells of the 

 gastric glands of mammals ? 



The conditions obtaining in the foregut of Proteus, Necturus, 

 and the larval Amblystoma are of interest apart from their 

 purely histological bearing. For it is obvious that, if the con- 

 dition in these animals is primitive, the gastric glands of the 

 ancestral types must have occupied a much more extensive 

 portion of the foregut than is the case in existing forms. 



Among fishes the subdivision of the foregut into oesophagus 

 and stomach is well marked, not only among the more highly 

 specialized Teleostomes, but also in the sharks and rays. No 

 glands are present in the oesophagus, and the epithelium is 

 different from that of the stomach. In Amia, Lepidosteus, and 

 Acipenser, according to Macallum (9), it is not only extremely 

 difficult to decide on superficial examination where the oesoph- 

 agus ends and the stomach begins, but on microscopic exami- 

 nation the former is found to have a similar epithelium to the 

 stomach and to contain glands. The nature of these glands is 

 at present in doubt. No doubt the investigation of the struc- 

 ture and histogenesis of the elements of the foregut in these 

 forms, and more particularly in Polypterus, will yield highly 

 interesting and instructive results. 



