98 P. W. GAMBLE, M.SC, AND J. H. ASHWORTH, B.SC. 



itself and loosely attached to the body- wall. The patches of " chloro- 

 gogenous" tissue are at first arranged in symmetrical oval areas right 

 and left of the dorsal blood-vessel, while more ventrally they are placed 

 in two or three less regular series, and are separated from one another 

 by a network of blood-vessels. 1 About the level of the tenth setae 

 these yellow areas all become subequal and arranged in a spiral manner, 

 ending at the level of the fourteenth setae. 



Stomach and Intestine. — The muscular wall of the gastric region is 

 exceedingly thin, and composed purely of circular fibres, which appear 

 to confer very slight powers of peristalsis upon the stomach. 



The mucus lining is strongly folded, and is composed of several 

 kinds of cells. 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 2 (PL IX., Fig. 23, Gv.) 

 is provided with specially long cilia, which produce a current of mucus 

 from before backwards. 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 mucus 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 somewhat as follows. 

 The sand or mud is mixed with the mucus 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 



1 This network is considered by Wiren and others to be parts of a continuous 

 sinus. We are not convinced, however, that this is really the case, and our 

 reasons will be found on p. 101 infra. 



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



