No. 3-] OESOPHAGEAL GLANDS OF URODELA. IOI 



even in a well-nourished animal. This is particularly the case 

 in those cells the inner ends of which exhibit signs of degenera- 

 tion in the shape of the structures described by Kingsbury as 

 mucous globules. It is probable that there is a tendency for 

 these glands in Necturus to degenerate rather than remain of 

 physiological importance. 



The so-called oesophageal glands of Proteus and Necturus 

 are really gastric glands the development of which has been 

 arrested. There is also in these animals an arrested develop- 

 ment of the foregut, compensation for which has been, in a 

 measure, attained bv the conversion of the anterior portion 

 of the stomach into a functional oesophagus. Only a short 

 anterior non-glandular portion actually corresponds to the 

 oesophagus of other Urodela. 



Two questions remain to be considered, the relation of these 

 glands to the oesophageal glands of higher vertebrates and to 

 the oesophageal glands of the frog/ 



The first question is a comparatively simple one. The oeso- 

 phageal glands of higher vertebrates have no features in com- 

 mon with those of Batrachia and are probably of secondary 

 origin. In Reptilia oesophageal glands are rare, and where 

 they do occur, as, for example, in Testudo graeca, are simple 

 crypts lined by cells similar to those of the surface epithelium, 

 namely, ciliated cells and goblet cells, the latter predominating. 

 In birds and mammals, where the epithelium is usually of the 

 stratified squamous variety, they are more or less complex 

 mucous glands. In no case, as far as I am aware, has investi- 

 gation revealed in the oesophageal glands of Sauropsicla or 

 Mammalia the occurrence of ferment-secreting cells. It is 

 probable that the oesophageal glands of higher vertebrates 

 have arisen in response to a demand, in a very long and rela- 

 tively narrow oesophageal tube, for a more efficient lubricating 

 mechanism, and an epithelium that will withstand friction. 

 The first step in this process is the formation of deep crypts 

 lined by ciliated cells and many goblet cells ; the second, the 

 disappearance of the ciliated cells from the crypts so as to 

 form a pure mucous gland, and their replacement on the sur- 

 face by a stratified squamous epithelium. 



