2t2 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



usually observed in fishes. In some respects these peculiarities may 

 be considered as due to a derivation accompanied by little dif- 

 ferentiation from structures which were probably present in the 

 primitive type of fishes. 



Of these, pouch-like deverticula of the epithelium in the oesophageal 

 portion of the fore- gut in the genera named, are in their inflated 

 portion wholly lined by flattened, almost squamous, epithelial cells, 

 each with a flattened nucleus and a quantity of clear protoplasm. 

 The cells in the neck of the pouch are cylindrical, strongly ciliated, 

 and but little differentiated from the common epithelial cells of the 

 oesophageal mucous membrane. The neck varies much in diameter 

 and length, being as a rule about half the diameter of the inflated 

 portion. Poixches of this description are most highly developed in 

 -Acijyenser, least so in Lepidosteus. It is impossible to say at present 

 what their function is, but I believe that it is transudatory. They 

 are not glandular in the present definite acceptation of the word, 

 and they cannot be for the purpose of absorbing digested food 

 taatter, since they are too far in front of the seat of digestive 

 changes. I have seen no description of like structures as occurring 

 in any other vertebrate. 



The oesophageal portion of the fore-gut in Amia and Acipenser 

 possesses glands similar to those found in the stomach in the same 

 genera, and which undoubtedly secrete pepsin. In this same part of 

 the fore-gut there are gland tubules which, in the cells lining them, 

 show all the degrees of differentiation from a simple epithelial crypt 

 to a fully formed peptic gland tubule. In the same two general 

 oesophagus and stomach act together as a digestive structure, both 

 being provided with peptic glands. In Acipenser the part of the 

 fore-gut which has hitherto been termed the oesopha,gus, possesses 

 taste-buds in large numbers and cannot, therefore, be rightly so 

 named. The part following it, and terminating behind the mouth of 

 the air duct, must, from the histological structure, be considered as 

 the oesophagus. 



The lining epithelium of the oesophagus in Acipenser and Lepidos- 

 teus, and that in oesophagus and stomach in Amia, is ciliated. In 

 all, the stomach possesses peptic glands of the type usual in fishes. 

 In Acipenser, glands of this character have been previously over- 

 looked, Leydig having described as such the ordinary epithelial 

 insinkings, or crypts, into which the true glands open. 



