372 W. S. NICKERSON. [Vol. XVII. 



flattened against one another, forming a rounded mass, but were 

 not perforated by a tubule, as Harmer believed to be the case 

 in L. crassicauda, and as Foettinger ('87) described in Pedicel- 

 lina. Furthermore, Prouho found two clusters of excretory- 

 cells on each side of the body, although he was unable to 

 make out a connection between them. 



My own observations accord much more nearly with those of 

 Prouho than with those of Harmer, Foettinger, and Davenport 

 ('93) on Urnatella. In L. Davenporti there is a pair of ciliated 

 (?) tubules opening into the atrium. Near the inner end of each 

 of these tubules is a rounded cluster of large vacuolated cells 

 appressed one against another so as to produce flattened sur- 

 faces of contact. Seen in the living animal, these cells show an 

 orange or reddish color, evidently due to the contained granules, 

 and the same color is present in the tubule to the exterior, 

 although a direct continuity of the color from the cells to the 

 tubule is not apparent. In the living animal I have not been 

 able to make out ciliary action in any part of the organ. A 

 second cluster of the large orange-colored cells is also present 

 at some distance from the excretory tubule (PI. XXXII, Fig. 

 4, ex.^ ex'.), but no connection between the two clusters has been 

 observed. PI. XXXIII, Fig. 33, shows the appearance of the 

 organ as seen in a section of an animal killed by corrosive-subli- 

 mate-formaldehyde mixture. The large excretory cells are very 

 highly vacuolated, the larger vacuoles containing a granular 

 coagulum, and the small nuclei appearing as though forced to one 

 side by the vacuoles. In this case each cell is bordered on one 

 side at least by a distinct space which partially surrounds the 

 cluster of cells. The duct to the exterior shows in this section 

 an irregular lumen, within which lies a cord of material which is 

 probably a coagulum precipitated by the reagents from the fluid 

 contained in the tubule. The walls of the tubule give faint 

 indications of being lined by fine cilia, though there is room for 

 reasonable doubt as to the correctness of this interpretation. 

 The lumen of the duct appears to communicate with the space 

 around the excretory cells. Though no connection has been 

 made out between the secondary cluster of excretory cells and 

 those here figured, it is nevertheless extremely probable that the 



