42 Mr Hardy and Mr Mc Dougall, On the Structure [Jan. 80, 



organ in the higher forms, Throughout the entire group the 

 existence of the three main divisions, stomodseum, mesenteron 

 and proctodseum, is very clearly seen, but whereas in the former 

 the mesenteron constitutes the greater part of the gut, in the 

 latter it is limited to a very short region into which the bile- 

 ducts open, and which forms only a very small fraction of the 

 total length of the alimentary canal. 



The long mesenteron of the lower forms exists as a simple 

 tube offering no obvious distinction into regions or diversity of 

 structure save the two so-called liver diverticula which spring 

 from its anterior end and extend forwards over the brain. 



The oesophagus or stomodseum is a short tube running up- 

 wards and forwards from the mouth to open on the ventral surface 

 of the mesenteric tube near its anterior end and a little posterior 

 to the points of origin of the liver diverticula which spring from 

 the lateral aspect. 



The proctodseum is rather longer than the stomodseum but 

 differs in this and other respects in the different divisions of 

 the Entomostraca. In the Phyllopoda it occurs as a short simple 

 tube. 



Though the mesenteron appears as a simple tube without 

 any obvious anatomical expression of differentiation of function, 

 yet a study of the processes of deglutition and digestion, and 

 of the character and arrangement of the cells lining its wall 

 makes evident the fact that in Daphnia this apparently simple 

 tube is divided into three regions, an anterior region devoted to 

 the absorption of the products of digestion, a middle region 

 wherein digestion occurs, and a posterior region in which the 

 faeces are formed. 



The fact that digestion occurs in a region of the gut posterior 

 to that which is occupied in the absorption of the products is 

 so far as we know without a parallel in the animal kingdom, 

 except perhaps among the simplest Coelenterates. 



For purposes of observation Daphnia can be readily fed by 

 pouring beaten yolk of an eg^, milk or carmine &c. over the 

 bottom of the dish in which it is living, and the phenomena 

 accompanying the taking in and digestion of food may be 

 easily followed in the living Daphnia owing to the transparent 

 nature of the animal. The various events will be described 

 in the order in which they occur. 



Deglutition is a rapid act. The food particles, e.g. carmine, 

 or yolk globules, are carried over the mouth in the current of 

 water which is constantly maintained by the movements of the 

 foliaceous appendages and many of them adhere to the sticky 

 surfaces of the mouth appendages. These adherent particles 

 are formed into a bolus by the movements of the appendages. 



