No. 3.] STUDY OF STENOSTOMA LEUCOPS O. SCHM. 291 



cells (Fig. 22). The cells at the base of the pit are much smaller 

 than those of the general integument. Each is 6 /i in length and 

 averages 2 /li in width. They are coarsely granular and at their 

 bases have large nuclei like those in the other epithelial cells. 

 No basal membrane could be distinguished apart from the mus- 

 cular layer {Mu.) which surrounds the pits. 



No cuticle was discovered at the outer ends of the basal cells, 

 but instead a thick homogeneous mass was seen to cover the 

 cells. The cilia of the epithelial cells could be seen passing 

 through this mass. In sections from a worm which was treated 

 by Kolliker's silver nitrate method this mass was seen closely 

 applied to the cells (Fig. 20, VV.). In chrom-osmic-acetic prepa- 

 rations it is somewhat shrunken away from the cells (Fig. 22, W.). 

 This mass is 3 /i thick. The cilia on the small cells at the base 

 of the pit are like those of the epithelial cells of the integument 

 except that they are very much longer. They range from 8 fx, 

 to 15 /Lt in length. The cells at the sides of the pits gradually 

 become larger and of the same character as those of the sur- 

 rounding epithelium. 



Graff ('82, p. 124) says that the ciliated pits of Microstoma 

 lineare and Stejwstoma leucops lie in front of the mouth, and 

 that they show a great variety of forms. Sometimes they appear 

 as long slits and sometimes as deep, cup-shaped pits. They are 

 not only a sinking in of the epithelial cells of the integument, 

 but of the muscular wall also. In Microstoma lineare their walls 

 are covered on the side toward the body cavity with a continuous 

 layer of pyriform cells which have round nuclei and dot-like 

 nucleoli. As Vejdovsky described a "zierliche Zellenrosette " 

 attached to the ciliated pits of Stejiostoma leucops, Graff con- 

 cludes that there is such a layer covering the ciliated pits of 

 Stenostoma also. 



Landsberg (S'jb, p. 5) agrees with Graff with regard to the 

 shape and position of the ciliated pits of Stenostoma Icncops. He 

 says that a nerve proceeds (probably) from the posterior gan- 

 glion lobe forward to a point just posterior to the pits, where it 

 divides and sends a branch to each pit. At the pit each of these 

 branches broadens out into a large ganglion which surrounds 

 the pit. 



In another paper ^Z^a, p. 170) Landsberg describes the his- 

 tology of the pits as he obtained it in sections of a worm which 



