420 HOPKINS. . [Vol. XL 



length varies in conformity to the inchned surface covered by 

 them (Fig. 7). 



In the writer's opinion this mode of transition may be re- 

 garded as a type to which, it is believed, most if not all of the 

 various groups of vertebrates will be found to conform. 



Edinger, whose investigations included Cyclostomes, Sela- 

 chians, one Ganoid (Lepidosteus), and many Teleosts, makes 

 this statement : " Where pavement epithelium is present, it 

 becomes thinner and thinner towards the stomach, the inter- 

 spersed beaker-cells increase in number and soon form a con- 

 tinuous stratum which extends over one or two layers of the 

 fiat cells, but at the border of the stomach lies directly upon 

 the connective tissue of the mucosa." 



In certain mammals (dog, cat) and in one reptile (soft-shelled 

 turtle) the transition from stratified to columnar epithelium has 

 been found to correspond to the above type, Gage (21). Extend- 

 ing from this point nearly to the pylorus, the epithelium is 

 ciliated (Fig. 12). For a short distance immediately beyond the 

 point of transition the mucous membrane appears very similar 

 to that at the pyloric end of the stomach; the epithelium is in- 

 folded, forming deep crypts, or follicles, which closely resemble 

 the pyloric glands; in the former, however, the epithelial cells 

 are ciliated, while in the latter they are not. The first few 

 crypts are lined by columnar ciliated cells only, but the true 

 glandular cells make their appearance before we reach the 

 opening of the pneumatic duct. In the latter case the tubes 

 are lined by two kinds of cells, the glandular cells occupying a 

 short segment at the base, and the ciliated cells the remaining 

 portion (Fig. 6). In many cases two or more glands open into 

 a common outlet. From the above facts the writer concludes 

 that the caudal portion of that segment of enteron which most 

 writers have called oesophagus is in reality a portion of the 

 stomach, a conclusion substantiated by Gegenbaur (22) and 

 Milne-Edwards (39). 



Stomach. — Although the stomach of certain of the stur- 

 geons has been investigated to some extent, no reference has 

 been found in the literature on the forms relative to an inter- 

 esting morphological feature found in the present species. 



