IB 



leo-ion (PL II., fig. 2), and roinniunicatiiig with tlio 

 exterior by a immher nf fine duets wliicli pierce the liodv 

 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, 

 t'.rd.). There are usually from to 12 on each side. It 

 otttMi happens that some of tlu> diicts are incomplete, the 

 portion which would ])ierce the circular muscle layer 

 being missing, though whether this is due to such ducts 

 being ntMv formations in cours(> of inward growtli fron) the 

 ectoderm, or whether they are commencing to atrophv is 

 an undecided point. 



It has beeii stated that the number of ducts increases 

 with the growth of the animal, from which it would 

 ai)peai- that such incomplete ducts belong to the 

 former of the above categoiies. 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 

 sjjecimen may possess a very much wider lumen than the 

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

 in which the numl)er of dm^ts increases, and then later a 

 period in which certain of the ducts enlarge, with the 

 result that others atrophy through disuse. Put the 

 ([uestion 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 (esophageal 

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

 blood lacunie become the lateral vessels and the 

 median dorsal vessel leaves the proboscis sheath. 

 Histologically th(> tubules consist of what would 

 })robably be styled cubical epithelium, were it 

 possible to distinguish the cell outlines. Its piotoplasiu, 

 which stains icadilv, is somewhat granular and contains 



