96 PROCEEDINGS OF THE AMERICAN ACADEMY 



free inner ends, which bear many sliort, thick, very active cilia. In sec- 

 tions the cilia are seen to be matted together into columnar masses, the 

 real nature of which may be learned by a comparison of a large number 

 of specimens. Among those cells are found a few (PI. II. ligs. 11, IG, 

 mc. gl.) that are larger and have less granular and less stainable con- 

 tents, and a smaller nucleus more centrally located. They are similar 

 to the cells found by Nasse {'S'2, p. 15) in the same position in Tubifex. 

 They were believed by him to be mucous glands (Schleimdriisen). 



The walls of the lower chamber have the cuticula and membrana 

 propria, and a layer of much flattened epithelial cells. The latter are 

 especially flattened in the anterior half of the pharynx, where the floor 

 of the lower chamber is therefore very thin. No cilia have been ob- 

 served on the walls of the lower chamber. Both longitudinal and cir- 

 cular muscular fibres are better developed on the pharynx than in any 

 other region of the alimentary canal, as is plainly to be seen in sec- 

 tions. They do not by any means, however, forrr> a continuous layer. 



Muscular fibres (PI. II. fig. 11, ?«?<•) also arise from the extreme 

 anterior wall of the first (head) segment, and are inserted into the 

 pharynx just beneath the middle of the supra-ocsophageal ganglion. 

 These, with other fibres running obliquely downward from the walls 

 of the mouth cavity to the body walls, both anteriorly and posteriorly, 

 serve as protractors of the pharynx. 



Covering and closely applied to the walls of the upper chamber 

 of the pharynx are found a large number of peculiar, more or less 

 rounded masses of cells (PI. II. figs. 11, \(J>,gl'.). These masses, or 

 clusters, are several cells deep, and lie in groups, the size of which is 

 determined by the frequency and position of the muscular fibres and 

 the processes from the connective-tissue cells above the pharynx. 

 The cells composing these masses have granular contents, and their 

 nuclei contain each only a single nucleolus. They are ellipsoidal in 

 shape, and their inner ends are frequently prolonged into j)rocesses 

 reaching toward the pharynx. Similar cells have been described by 

 Nasse ('82, p. 15) in Tubifex. On account of their position, and of 

 their being divided into groups, they are regarded by him as digestive 

 glands. He saw no opening, however, leading from them into the 

 alimentary canal. In two instances I have been able to trace a pro- 

 cess from one of these cells passing through the layer of epithelial 

 cells to the pharyngeal cavity. Hence it seems probable that all these 

 cells open into the cavity of the pharynx ; but whether they have a 

 digestive function is still open to question. 



The largest of the connective-tissue cells are found above the pha- 



