252 Miss R Alcoclc, On the Digestive [Nov. 9; 



(3) Exhibition of Phylloxera vastatrix. By A. E. Shipley, 

 M.A., Christ's College. 



Professor Hughes in the Chair. 



(4) The Digestive Processes of Ammocoetes. By Miss R. 

 Alcock (communicated by Dr Gaskell). 



[Received December 3, 1891.] 



In all the higher vertebrates digestion is carried on by means 

 of the secretion of specialised glands localised in certain definite 

 portions of the alimentary canal or of glandular masses which are 

 formed as appendages of the same. The formation of a peptic fer- 

 ment is confined to the glands of the stomach, of a tryptic ferment 

 to the pancreas and of diastatic ferments to the salivary glands and 

 pancreas. Passing to lower forms we find in Amphibia that the 

 formation of peptic ferment is not restricted to the stomach, but 

 extends oralwards into the oesophagus, which is even more active 

 as an organ for digestion than the stomach. Then in Fishes this 

 tendency to diffuseness in the position of the proteid-digesting 

 glands is even more pronounced, and it is remarkable, as Kruken- 

 berg has pointed out, how their position varies even in nearly 

 allied families. Sometimes a pancreas is present, sometimes 

 absent; in some the appendices pyloricae are well developed, in 

 others they do not exist, and in some they function as digestive 

 glands, whilst frequently they seem merely to act as organs of 

 absorption. In some cases the so-called pancreas does not func- 

 tion in proteid digestion, and in many fishes certain cells forming 

 part of the liver secrete a tryptic ferment, which enters the ali- 

 mentary canal by means of the bile-duct. The pepsin-forming 

 glands also vary in position, sometimes extending oralwards and 

 sometimes into the upper part of the intestine. 



These observations of Krukenberg lead to the conclusion that, 

 as far as digestive organs are concerned, the lower we descend in 

 the scale of evolution of the vertebrates, the greater is the ten- 

 dency towards a decrease of specialisation in function and a diffuse- 

 ness in the position of the secreting cells. If this is the case, the 

 study of the digestive processes in the lowest vertebrates ought to 

 shew this absence of concentration of the secreting tissues in a still 

 more pronounced manner. With this object Dr Gaskell proposed 

 to me to find out how the digestive processes were carried on in 

 the Ammocoetes, as no physiological observations have been made 

 on the digestion of this primitive vertebrate by Krukenberg or any 

 other observer. 



