ON THE NEPHRIDIA OP THE POLY0H.^TA. 447 



of which extends the lip of the ciliated organ (figs. 16, 17, and 

 30). 



The latter division, which I shall call the csecum, extends 

 between the nephridial duct and the main limb of the ciliated 

 organ. It is best developed in Gl. unicornis. 



On examining this caecum more closely its cavity is found 

 to be subdivided by means of thin walls, formed apparently by 

 folds of the epithelium, projecting inwards from the side 

 opposite to tiiat on which the ciliated organ is situated (figs. 19, 

 20, and 30). The chambers thus formed, resembling somewhat 

 the cells of a honeycomb, are partially, but not entirely, cut off 

 from the main cavity by roofing extensions of the walls (fig. 

 19). 



At the blind extremity of the caecum the chambers become 

 small, and disappear near the ciliated epithelium. At the 

 opposite open end they extend into the main cavity of the sac, 

 becoming more and more shallow, and soon dying out (fig. 30). 



The contents of the sac will be described below. 



On the Functions of the Ciliated Organs, Nephridial 

 Sac, and Nephridium, and on theCoelomic Fluid of the 

 Glyceridse. — The functions of the organs forming the nephri- 

 dial complex are no doubt connected with excretion. When 

 the worm attains sexual maturity the ciliated organ probably 

 acts as a genital duct; of this, however, I have no direct proof, 

 and the discussion of the matter must be reserved for a future 

 paper. 



The nephridium itself is of course a kidney excreting waste 

 matter. In freshly killed specimens the walls of this organ 

 are found, as already mentioned, to be full of dark granules 

 and paler droplets of varying size, which sometimes flow 

 together, forming quite large drops embedded in the proto- 

 plasm. As might be inferred from the fact that the nephridium 

 does not communicate with the cojlom, it seems to be entirely 

 concerned in the excretion not of solid particles, but of substances 

 dissolved in the coelomic fluid. These appear to be stored up 

 as granules and droplets, which are subsequently discharged 

 into the lumen of the nephridial duct. 



