No. 2.] ENTERON OF AMERICAN GANOIDS. 419 



Oesophagus. — In his work on the " Fishes of France," Moreau 

 (41) says of Acipenser: "The oesophagus is covered or armed 

 with papillae more or less conical and directed backwards. The 

 stomach is scarcely larger than the oesophagus; it would be diffi- 

 cult to establish the line of separation if the gastric mucosa did 

 not present a different appearance, it being entirely smooth. It 

 is at the commencement of the stomach, a little back of cer- 

 tain small pad-like structures formed by the termination of the 

 oesophagus, that the canal of the air-bladder opens." Ryder 

 recognizes in the alimentary canal three very clearly defined 

 regions. Of these the first, or oesophageal, " extends as far 

 back as the opening into the air-bladder. The gullet proper, 

 . . . upon being laid open, is found to be covered for some 

 distance with backwardly-directed soft fleshy processes, into 

 which its mucous membrane is elevated. At some distance in 

 its course farther back, its lining membranes again become 

 smooth, but slightly folded longitudinally." With but one or 

 two exceptions all the authors mentioned in this paper, who 

 have expressed themselves on the point, state that the pneu- 

 matic duct opens into the oesophagus. The epithelium of the 

 latter, according to Leydig (33) and several others, is like that 

 of the buccal cavity, a stratified pavement epithelium. So far 

 as noted, all authors say that there are no glands in the oesoph- 

 agus. From the above quotations it will be seen that the 

 stratified pavement epithelium extends backward to the open- 

 ing of the pneumatic duct, and that this region is non-glandu- 

 lar. The correlation of the parts, as found by the writer, is 

 somewhat at variance with the above statements. In my speci- 

 men, an adult sturgeon about two metres (six feet) in length, 

 the stratified epithelium, together with the fleshy papillae, dis- 

 appear at a point about 5 cm. in front of the pneumatic duct 

 opening. Succeeding the stratified is a columnar epithelium 

 which extends uninterruptedly to the pylorus. Considered 

 from a mechanical standpoint, almost every one would say that 

 the stratified should overlap the columnar epithelium, but 

 the exact reverse is the case. At the transition point the 

 stratified epithelium becomes obtusely wedge-shaped ; the 

 deeper layers are overlaid by cylindrical-shaped cells whose 



