248 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



shaped cells of the excretory portion of the uephridium, 

 which, even in young specimens, contain some excretory 

 granules. Sections of the nephridia of young specimens 

 show that the cells lining this part of the organ bear one 

 or two long cilia on their inner ends, and that their some- 

 what vacuolated protoplasm contains comparatively few 

 concretions (fig. 30). In older specimens the concre- 

 tions in the cells are very numerous, filling up the middle 

 and part of the distal region of the cell. The granules 

 are either black or yellowish, and some at least consist 

 of acid-urate of sodium (Willem). The distal fourth of 

 the cell is almost free from granules ; they appear to have 

 been extruded into the cavity of the nephridium. Con- 

 siderable collections of such yellow ' granules are 

 occasionally found in the lumen of the organ. Finely 

 powdered carmine, when injected into the ccelom, is taken 

 up by the cells lining the excretory portion of the nephri- 

 dium, and afterwards extruded in small masses. Below 

 the excretory epithelium there is a thin, almost structure- 

 less, layer of connective tissue, while in the walls of the 

 vesicle there is a thin layer of muscle fibres in a corre- 

 sponding position. In young specimens the cells lining 

 the vesicle contain fewer granules than those of the 

 middle part of the nephridium ; but in old specimens 

 there is little difference in this respect between the cells 

 of the two regions. 



The network of blood-vessels with which the nephri- 

 dium is provided lies between the excreting epithelium 

 and the thin ccelomic epithelium which covers the organ. 



From the dorsal vessel a branch is given off which 

 runs on the anterior face of the first diaphragm. This 

 divides — one part supplies the body Avail in the region of 

 the third setal sac, and is there connected with the longi- 

 tudinal dorsal vessel ; the other part enters the funnel of 



