58 



o])eiiiiig to the exterior. Tlie excreiovv papilUe of the 

 kidneys have a small central canal lined by ciliated 

 epithelium, outside which is a fairly strong- ring- of 

 circular muscle. The blood supply of the kidneys has 

 already been spoken of in the account of the circulation, 

 to which reference should be made. 



The pei^cardial communication of this rig-ht kidney 

 has often been discussed, the difficulty of observation 

 having- led to the enunciation of conflicting- opinions by 

 different Avorkers. It is generally admitted that the 

 reno-pericardial canal opens into the sub-rectal lobe of 

 the kidney, but the exact position of this opening, and 

 the length of the canal, are subjects of dispute. 

 Cunningham makes the canal open into the dorsal 

 surface of the sub-rectal lobe some distance to the left 

 of the rectum, while Goodrich and Pelseneer find the 

 opening on the ventral surface of that lobe i)ractically 

 ventral to the rectum. Our results (hg. ^Jl) support the 

 latter view, and we find that the long canal opens into 

 the extreme right end of the pericardium. Most of our 

 sections differ somewhat from those of Pelseneer and 

 Goodrich as regards the space relations of kidneys, peri- 

 cardium and nuchal cavity, but we think these relations 

 vary a good deal in different specimens, and also change 

 somewhat with the age of the individual. 



Reproductive OiuiAxs. 



The gonad occupies the ventral face of the left side of 

 the visceral mass (figs. G, 8) in both sexes. It varies very 

 much in size at'different seasons. In a very young form 

 it is practically a pouch, the cavity of which is coelomic. 

 This cavity is lined by germinal epithelium, which, with 

 its underlying tissue, grows in as folds, some of which 

 unite into trabecula' (fig. o'-ya), thus converting the pouch 



