HEKATEROBEANOHUS SHRUBSOLII. 181 



(fig. 2). Its anterior part is avertible and richly ciliated. It 

 is almost always extruded at once when the animal is first 

 compressed by a cover slip (fig. 3, B.ph.). The pharynx narrows 

 in the posterior part of the 2nd segment to form the 

 oesophagus^ which is continued through the next few segments. 

 The canal then gets much wider, and begins to be constricted 

 intersegmentally by the septa. The segment in which this 

 change from oesophagus to intestine takes place varies with 

 the size of the individual. Posteriorly, i.e. in the posterior 

 third or fourth of the body (again varying according to the 

 size of the individual), it narrows again, and this part espe- 

 cially is exceedingly contractile. The anus is terminal (fig. 

 2). From it cilia can be seen moving upwards towards the 

 mouth, indicating thereby some anal respiration. In some 

 specimens, but not in all, ciliated ridges could be seen in the 

 intestine just in front of the anus (fig. 11), probably the same 

 thing as the richly ciliated swelling found in the larvae of allied 

 forms. The alimentary canal is lined throughout by columnar 

 epithelium, consisting of cells one layer deep, ciliated in the 

 pharynx and oesophagus, and also in the hinder unconstricted 

 part, of the intestine, but apparently not in the anterior con- 

 stricted part, which occupies the greater length of the body. 

 This epithelium is much folded in the anterior region^ especially 

 in the pharynx (fig. 5, int. ep.), not so much in the third 

 and fourth segments, but again in the hinder oesophageal 

 region. It is not folded, and the lumen of the canal is wide, 

 in the anterior intestinal region (fig. 6) ; afterwards it again 

 becomes folded to some extent (fig. 7) . The cells forming the 

 folds are longer and narrower than the others (figs. 5 and 7), 

 but their nuclei, as in the other cells, are situated close to the 

 peripheral wall, all the nuclei together forming a very regular 

 circular layer. 



Outside the epithelial layer is a very thin circular muscular 

 layer, best seen in the anterior region of the body (fig. 5, c. wr.), 

 but not seen at all distinctly posteriorly, though its presence 

 would seem to be indicated by the muscular contractions of the 

 whole alimentary canal. There are no longitudinal muscles to 



