332 THE EARTHWORM chap. 



attached to the posterior faces of the septa. Each 

 nephrostome (a) is cihated, and projects through the cor- 

 responding septum so as to communicate with the segment 

 of the body-cavity next in front of that in which the main 

 part of the tubule is situated. The nephrostome opens into 

 a long and slender transparent part of the tube lined with 

 ciliated cells in part of its course and extending along the 

 first and second loops (l)) ; this part is succeeded by a 

 wider, ciliated portion in the second loop {c), which com- 

 municates with a still wider portion {d) lined by granular, 

 non-ciliated, glandular cells, also lying in the second 

 loop ; the glandular portion opens to a much wider 

 muscular part of the tube {e) which constitutes the third 

 loop and opens into the exterior by a small pore — the 

 nephridiopore — near the outer seta of the inner couple 

 (Fig. 78). 



Thus the nephridia, which are abundantly supplied with 

 blood-vessels, are lined in part by gland-cells and in part 

 by cilia which work towards the exterior. Water and 

 nitrogenous waste from all parts of the body pass by diffu- 

 sion into the blood and are conveyed to the nephridia, 

 the gland-cells of which withdraw the waste-products and 

 pass them into the cavities of the tubes, whence they are 

 finally discharged from the body. The granular yellow cells 

 on the walls of the intestine also appear to contain ex- 

 cretory products, which become iet free in the body cavity 

 and are thence got rid of through the nephridia. It will 

 be noticed that a certain amount of loss of the coelomic 

 fluid must take place through the dorsal pores as well 

 as through the nephridia. 



In discussing the hydroid polypes we found that one of 

 the most important points of difference between the loco- 

 motive medusa and the fixed hydranth was the presence in 



