THE LAMPREY. 15 



the anus (a). The intestine is quite free for the greater 

 part of its length, but at its hinder end is attached to the 

 dorsal wall of the body-cavity by several delicate mesen- 

 teric bands, carrying blood-vessels, while in front it is 

 firmly connected by fibre with the anterior half of the dorsal 

 surface of the liver. 



40. The kidneys (Figs. 5 and 7, k), two elongated 

 band-like organs, of a deep red colour, attached by peri- 

 toneum one on each side to the dorsal wall of the body- 

 cavity, and extending from about the middle of the latter to 

 within a short distance of the anus. 



41. The ureters (Figs. 5 and 7, #;), delicate tubes as 

 wide as, or wider than the intestine, and attached all along 

 the free (outer or ventral) edge of the kidneys: passing 

 backwards they become connected with 



42. The urinogenital sinus (Fig. 5, ti.g.s), a small 

 ovoidal sac, lying close behind the rectum, and becoming 

 narrowed ventrally to form the urinogenital papilla 

 (u.g.p). 



43. The sub-vertebral lymph sinus (Fig. 7, ly), a considerable 

 cavity included between the layers of peritoneum supporting the kidneys 

 and genital gland : it is divided into two by a median vertical partition. 



44. Note also the pericardium (Fig. 4, pc), lying just 

 in front of and partly covered by the liver : its almost 

 hemispherical posterior wall, strengthened by cartilage 

 ( 1 8, Fig. i) pc) is all that can be seen at present. 



VI. Open the urinogenital sinus by carefully slitting up its left 

 wall, first introducing a guarded bristle x by the external 

 aperture : observe 



45. The apertures of the ureters (Fig. 5, x, x'), situated close 

 together in the antero-dorsal region of the sinus. 



1 That is, a bristle tipped with a small knob of sealing-wax. 



