170 WM. A. KEPNER AND W. H. TALIAFERRO 



surface of the syncytial wall bears stout cilia. If nothing more 

 could be said of this pit than that it is an organ whose wall is 

 composed of ciliated cells, no departure would be made from the 

 prevalent conception of the anatomy of the ciliated pits of flat 

 worms. However, all of the wall of the ciliated pit does not 

 bear cilia, nor is the cytoplasm of uniform density. The con- 

 tinuity of the cilia is broken by two ridges which lie more or less 

 parallel to the axis of the pit. These ridges do not bear cilia and 

 their cytoplasm is denser than that of the general wall of the 

 organ (figs. 3 and 4, SR, and fig. 6). This ridge of cytoplasm 

 is most prominent and densest over the middle nucleus of each 

 side (fig. 6, C). Correlated with this the cytoplasm surrounding 

 this nucleus receives the most extensive nerve supply (fig. 3, 

 A^, and 7, C). The middle nucleus of each side therefore, and 

 its adjacent cytoplasm we consider to represent the sensory 

 region of the ciliated pit ; the four remaining elements of the 

 syncytium being the accessory cells (fig. 6, B and D). The 

 nerve which runs to this sensory region is a branch of the an- 

 terior trunk given off from the dorsal ganglia. 



The sensory ridges or rods, however, do not constitute the 

 feature that makes these pits most depart from the prevalent 

 conception of these organs of flat worms. There is in addition 

 to the six cells above referred to, a seventh. This is a gland 

 cell (figs. (3 and 7, GC), which lies over the fundus and communi- 

 cates with the lumen of the pit by means of a varying number 

 of ducts, which pass through the wall of the pit on the anterior 

 angle of its fundus (figs. 2, 5, 6 and 7, GP). The contour of this 

 unicellular gland is quite irregular and the cell gives off an incon- 

 stant number of diverticula. Within the cytoplasm are refrac- 

 tive granules which take, with Bordeau red, a bright, reddish 

 yellow tint, marking them in a manner peculiar to this uni- 

 cellular gland. Though we here commit ourselves to the con- 

 cept that this is a unicellular gland, its contour is so irregular 

 and its limits are so poorly defined that it is quite possible that 

 other nuclei, which belong to this grandular region, have been 

 overlooked. However, there are associated with the general 

 epithelium of the body, numerous unicellular glands, which. 



