14 F. W. GAMBLE AND J. H. ASHWORTH. 



gastric region is exceedingly thin, and composed purely of 

 circular fibres, which appear to confer very slight powers of 

 peristalsis upon the stomach. 



The mucous lining is strongly folded, and is composed of 

 several kinds of ceils. Some of the cells in all parts of the 

 stomach are ciliated, others are apparently digestive, and a 

 large number appear to secrete a mucus similar to that of 

 the oesophagus, the cells themselves being discharged into the 

 mucus which they help to form. 



Commencing about the middle of the stomach (that is 

 between the ninth and tenth segments) is a ventral groove 

 formed by a couple of folds of its inner and lower surface. 

 This groove^ (Pi. 4, fig. 23, Gv.) is provided with specially 

 long cilia, which produce a current of mucus from before back- 

 wards. There are other smaller grooves on the side walls of 

 the stomach and the anterior part of the intestine, whose 

 general direction is downwards and backwards, and which 

 open into the median ventral groove. The direction of the 

 current in all these is from before backwards. The ventral 

 groove is continued back to the anus. The intestine is dark 

 brown or nearly black in colour externally. Its mucous lining 

 is somewhat similar to that of the stomach, but is covered by 

 a thin cuticle, and is not ciliated. 



The process of digestion in the lugworm has not been at all 

 fully investigated, but the series of events appear to be some- 

 what as follows. The sand or mud is mixed with the mucous 

 secretion of the oesophagus, and is slowly carried backwards by 

 peristaltic contraction. At the junction of the stomach and 

 oesophagus the secretion of the oesophageal pouches is poured 

 upon the sand. Wiren regards the contents of these pouches 

 as acid and digestive. In several cases we have found the fluid 

 neutral. In the stomach several changes occur. The secre- 

 tion of the gastric cells proper is probably digestive, and this, 

 together with a further amount of mucus, is mixed with the 

 sand, and shaken together by the swing of the loose gastric 

 loop. In this way the food, which apparently consists of the 

 ' This groove has only hitherto been noticed by Wiren (1887). 



