ON PHYMOSOMA VARIANS. 83 



fibres by the fusion of the anterior and posterior muscles of 

 the left and right side respectively. These lateral bundles 

 have fused with the oesophagus, a small amount of gelatinous 

 connective tissue containing branched cells being found be- 

 tween them and the circular muscles of the oesophagus. The 

 dorsal blood-vessel lies between the lateral muscles in a 

 groove,, closely applied to the dorsal side of the oesophagus 

 and extending back almost to the beginning of the intestinal 

 coil. 



Owing to the presence of very fine sand in the intestine and 

 the delicacy of the tube which make it impossible to satis- 

 factorily wash the sand out, I had considerable difficulty in 

 studying the histology of this part. The intestine is lined 

 throughout by a layer of columnar epithelial cells, one cell 

 thick. The nuclei of these cells are situated near the base. 

 Outside this layer is a thin membrane in which muscle-fibres 

 are sparsely scattered. I do not think the intestine is uni- 

 formly ciliated, but patches of cilia occur here and there. 

 The arrangement of these ciliated patches I failed to make out. 

 There is no groove with long cilia running the whole length of 

 the animal, such as has been described by Keferstein in 

 Sipunculus. 



The lumen of the rectum is almost occluded by the presence 

 of numerous folds projecting into it. These folds are covered 

 with a number of columnar cells some of which are ciliated, 

 but the majority are crowded witli large vacuoles containing 

 minute granules ; these are devoid of cilia. Tlie rectum has no 

 CJEca opening into it, such as are found in Sipunculus. 



The external cuticle is folded into the anus for a little way, 

 and the circular muscle-fibres of the body wall are thickened 

 around the anus in this region, forming a very efficient 

 sphincter. A number of radially arranged fibres also pass out 

 all round the anus ; these fibres are derived from the longi- 

 tudinal muscles. Their action is obviously antagonistic to that 

 of the .^sphincter. 



