186 



Transactions. 



bridge canal. Thence the long cilia in tliis region carried the excretory 

 products into the ampidla and wide tube. 



The ciliation stops just before the dilatation which forma the ampulla ; 

 the cilia, at the end are much longer, and have the form of a whip or flame 

 which projects into the cavity of the dilatation (fig. 10, «;). They do not 

 fuse to form the whip, though the appearance presented in the living ne- 

 phridium would indicate a fusion, for the vibration of the cilia is very rapid, 

 and they vibrate in unison, imdulations passing from end to end in rapid 

 succession, as in the flame-cells of the Platylielmia. When the vitality 

 becomes more feeble, however, the action becomes slower, and the Separate 

 cilia now vibrate individually, revealing the real structure of the flame. 



The extraordinary vitality of the tissues is demonstrated by the fact 

 that cilia were still moving briskly in the nephridium of a worm which had 

 been killed in weak alcohol and dissected three days previously. They 

 were still sufficiently active to indicate clearly the direction of the current 

 in the nephridial canals. 



Histology. 



rhe nephridium has a continuous covering of flat coelomic epithelial 

 cells (fig. 6, ep). This epithelium is indicated by the small darkly staining 

 nuclei, which cover the whole nephridiimi and the blood-vessels connected 

 with it. 



The irregular outlines of the angular epithelial cells are very easily seen 

 in uephridia from a worm preserved in acetic-bichromate. The nephridia 

 may be mounted whole in glycerine, which 

 shows clearly the boundaries of the separate 

 cells, while the nuclei shine out coiiispicuously. 

 The epithelium was jiarticularly well seen in 

 this way on the bladder, as shown in fig. 6, 

 where the cells are only partly filled in. The 

 muscle-fibres seen in the figure shine through 

 the flat cells ; below these again are seen the 

 nuclei of the epithelium bounding the lumen 

 of the sac. 



I have remarked on the fact that the pave- 

 ment coelomic epithelium is so easily shown 

 on the bladder of MaoridrUus because it ap- 

 pears to be so difficult to demonstrate (ui the 

 musculai' sac of other genera. 



In Mouiligaster grandis, for instance, 

 ^ Bourne has said that there is a layer of 

 pavement epithelial cells over the bladder, 



but that these are very delicate, and there- b^iG. H. -Section through a nephri- 

 fore difficult to demonstrate ; while in 

 Lumbricas Benham was unable to find a 

 continuous epithelium outside the muscular 

 coat, and was of the opinion that the 

 granular protoplasm of the bladder-wall in 

 which the muscle-fibres are embedded repre- 

 sented not only the vesicular connective 

 tissue, but also the coelomic epithelium. 



To continue now the description of the structure of the bladder (see 

 fig. II). Below the ])avement-cells is a layer of granular protoplasm con- 





Uopore, drawn (under the oil 

 immersion) from:[a-[series of sec- 

 tion.s through the'posterior part 

 of the worm. J The figure show.s 

 the third ' pore from the pos- 

 terior end. Thfi ii-regularity of 

 the lining of the bladder is due, 

 no doubt, to the contraction of 

 the muscular wall. 



