254 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



region (PL II., fig. 2), and communicating with the 

 exterior by a number of fine ducts which pierce the body 

 wall and open laterally above the level of the lateral nerves. 

 The number of ducts varies both in different specimens 

 and on the two sides of the same specimen (PI. IV., fig. 1, 

 exd.). There are usually from 6 to 12 on each side. It 

 often happens that some of the ducts are incomplete, the 

 portion which would pierce the circular muscle layer 

 being missing, though whether this is due to such ducts 

 being new formations in course of inward growth from the 

 ectoderm, or whether they are commencing to atrophy is 

 an undecided point. 



It has been stated that the number of ducts increases 

 with the growth of the animal, from which it would 

 appear that such incomplete ducts belong to the 

 former of the above categories. On the other hand, 

 the writer's own experience is that a large specimen may 

 have but half as many ducts as one considerably smaller, 

 though in such a case certain of the ducts in the large 

 specimen may possess a very much wider lumen than the 

 rest. Consequently it is quite likely that there is a period 

 in which the number of ducts increases, and then later a 

 period in which certain of the ducts enlarge, with the 

 result that others atrophy through disuse. But the 

 question is one that requires more fully working out. 



The excretory tubules commence not far behind the 

 mouth, and extend almost to the end of the oesophageal 

 region (PI. IV., fig. 1). Directly they cease the lateral 

 blood lacunae become the lateral vessels and the 

 median dorsal vessel leaves the proboscis sheath. 

 Histologically the tubules consist of what would 

 probably be styled cubical epithelium, were it 

 possible to distinguish the cell outlines. Its protoplasm, 

 which stains readily, is somewhat granular and contains 



