TTJBIFEX. 343 



often be seen in motion. If the tube be removed from 

 the body, the cilia very quickly cease to move, and it is 

 impossible then to decide whether any particular portion 

 of the tube is ciliated or not (PI. VI, fig. 43). 



The nephrostome is small and very simple in 

 structure. Its diameter in the widest place is only 

 slightly greater than that of the nephridial tube. Its 

 lumen is a little larger than that of the tube, and its walls 

 are somewhat thicker, making it funnel-shaped. It is 

 composed of a very few cells, the nuclei of which are 

 large, round and nucleolated (PL VII, fig. 47). The 

 inner borders of the cells, those abutting on the lumen, 

 are ciliated, the cilia being long and pointing chiefly in 

 one direction, namely, from the free end of the funnel 

 down the tube. Some of the cilia, however, fringe the 

 free edge of the funnel, and these are particularly long 

 and very active. By their rapid movements they create 

 a current in the direction of the funnel, into which the 

 excretory products are drawn. The pre-septal part of the 

 tube is extremely short and uncoiled, and its cavity is 

 directly continuous with that of the funnel. Its walls are 

 thin, and the nuclei of the cells are flattened in a direction 

 parallel to that of the tube. The tube is ciliated in this 

 part. % 



The post-septal portion of the nephridium can be 

 sub-divided into three regions: — (1) A delicate, much- 

 coiled tube with extremely thin walls. (2) This passes 

 into a slightly thicker walled tube of a yellowish colour, 

 and decked with specially modified peritoneal cells. 

 (3) This again passes into a somewhat thinner walled 

 tube, which is covered with specialised peritoneal cells 

 for part of its length, and which finally opens into a small 

 vesicle communicating with the exterior at the nephridio- 

 pore (PI. VI, fig. 43, t.). 



