98 PROCEEDINGS OP THE AMERICAN ACADEMY 



layer; but, while the greater portion of the cells remain destitute 

 of cilia, aud form a more or less continuous layer next to the mera- 

 brana propria, there are other, less numerous cells, which project far 

 into the lumen of the canal aud are richly ciliate at their free ends. 

 They are of various shapes, the basal ends being often produced into 

 two or more diverging processes, which thus give the ciliate cells the 

 appearance of spanning one or more of the cells of the non-ciliate 

 layer. Although in many instances they appear to arise from the free 

 surfaces of the latter, it is only a deceptive appearance, since their 

 processes really extend to the membrana propria. They are to be 

 regarded as the effect of a differentiation whicli results in an increase 

 in tlie amount of surface exposed to tlie aliment, and at the same, time 

 relegates to a few cells the function of propelling the food along the 

 canal. This peculiarity serves as a ready means of distinction be- 

 tween oesophagus and intestine, and is most apparent in cross sections. 

 Similar, but not identical cfcUs have been observed by Timm ('83, 

 p. 148) in Nais elinguis. 



A few epithelial glands have been seen in the oesophas^us in the 

 ninth, tenth, and eleventh segments, but as a rule they are absent from 

 the ojsophagus, while abundant in the intestine. 



The intestine extends from near the partition between the eleventh 

 and twelfth segments to the anus. It is distinguished from the oesoph- 

 agus by the characters mentioned above. The tube grows suddenly 

 larger in the twelfth segment, and then gradually tapers to the anus, 

 being slightly constricted at each partition in the fore part of its 

 course. The part of it following the oesophagus has cither very short 

 cilia or none at all. Farther back the cilia become longer, and near 

 the anus they almost fill the canal. 



Many endodermal glands (PI. III. fig. 28, en. gl.) are found scat- 

 tered throughout the epithelium of the intestine. They are unicellular 

 and jug-shaped, usually somewhat larger than the neighboring endo- 

 dermic cells of the same region. Sometimes they appear empty, but 

 usually they are filled with a granular non-stainable material, or con- 

 tain a nodule of such substance near the centre. Each opens into the 

 interior of the intestine by a narrow canal, which is frequently visible 

 in sections. 



The liver cells are lens-shaped, with a large nucleus containing a 

 single nucleolus. They are closely applied by one of their broader 

 surfaces to the wall of the alimentary canal, just outside the layer of 

 blood-vessels with which the latter is immediately invested, and which 

 can be well seen only in certain longitudinal sections. Over a part of 



