The Microscope. 211 



As the three authors named stand very high as original inves- 

 tigators, as the work of one of them (Wiederscheim) was pub- 

 lished in 1883, and as no original work upon this subject has 

 been done, so far as I know, since their publication, their state- 

 ments may be taken as representing the present state of knowl- 

 edge upon the subject. 



In Necturus, one of the water salamanders with permanent 

 external gills, found in ail the larger lakes and streams west of 

 the Hudson river, the lining epithelium of the oesophagus is col- 

 umnar and ciliated, but that lining the mouth is not a ciliated 

 but a stratified, pavement or transitonal epithelium. The cells 

 are very large and irregular, and possess a large nucleus which 

 show quite clearly what is considered by many writers to be an 

 intra-nucleur net-work, and also a clear zone (nuclear-mem- 

 brane) separating the nucleus from the cell-body. In meno- 

 poma — the large water salamander without gills, found in the 

 Alleghany and Ohio Rivers — the structure of the epithelium of 

 the mouth and oesophagus is as described for necturus. 



While the facts presented in this paper show the danger of 

 generalization with reference to a specific structure or function, 

 unless all the facts that may support or overthrow the general- 

 ization have been critically investigated ; they also suggest what 

 seems to be a fruitful field of inquiry ; viz, to see what mode of 

 life or general advancement in structure is accompanied by a 

 ciliated epithelium both in the mouth and in the oesophagus, as 

 in the frog; and also the conditions under which the mouth is a 

 non- ciliated, and the oesophagus a ciliated epithelium. The 

 mode of life and the structural conditions in necturus and meno- 

 poma point to the generalization that while in all amphibia the 

 oesophagus is probably lined with columnar ciliated epithelium, 

 the epithelium lining the mouth is columnar and ciliated in the 

 forms living mostly on the land or on the surface of the water, 

 and into whose mouth water only occasionally finds access (frogs, 

 toads, many salamanders) while in these, like necturus and 

 menopoma, living almost exclusively under water like a fish, 

 the epithelium of the mouth is non-ciliated and stratified. [Read 

 before the American Society of Microscopists at Cleveland.] 



