236 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



fourteenth seta? they are either indistinct or absent. The 

 epithelial lining of the stomach is strongly folded. It 

 consists of columnar cells among which are numerous 

 goblet-like cells, some of which produce a secretion which 

 is probably digestive, while others form mucus (fig. 51). 

 Commencing near the middle of the stomach, i.e., about 

 the level of the ninth seta?, there is a well-marked ventral 

 groove, the cells lining which are provided with long cilia 

 which produce a current from before backwards (fig. 36). 

 There are numerous smaller ciliated grooves on the lateral 

 walls of the stomach and intestine in which the flow is 

 downwards and backwards into the ventral groove. The 

 ventral groove extends to the anus. The intestine is 

 lined by columnar cells, ciliated in the above mentioned 

 grooves, among which only a few gland cells are present. 



Circular and longitudinal muscle fibres are present 

 in the walls of the alimentary canal, but they are well 

 marked only in the oesophagus ; in the stomach and intes- 

 tine they are so feebly developed that these parts of the 

 alimentary canal can have only slight powers of 

 peristalsis. 



The process of digestion has not been fully investi- 

 gated, but the series of events appears to be somewhat 

 as follows: — During life the buccal mass and pharynx 

 are constantly being everted and withdrawn, carrying 

 sand into the oesophagus. As the sand passes along the 

 oesophagus it is mixed with the mucus from the cells 

 lining this part of the gut, and further back the secretion 

 of the oesophageal glands is poured upon it. The mixture 

 then passes into the stomach, where the secretion from 

 the mucus-forming and digestive cells is added to the 

 mass. The swinging backwards and forwards of this part 

 of the alimentary canal, brought about by the muscles of 

 the body wall and by the protrusion and retraction of the 



