58 



the great vena cava ; and the blood in the vena cava thus 

 penetrates into this intricate system in the appendages on 

 its way to the gill. Now externally these appendages are 

 covered by the glandular wall of the kidney, as they 

 encroach on the cavity of the kidney sac. They show 

 many furrows and minute holes on their external surface, 

 which are lined by the glandular kidney epithelium. 

 Hence the blood contained in the vascular network in the 

 appendages comes into intimate connection with the 

 glandular cells of the kidney, and is deprived of its 

 excretory products. The appendages are spongy and 

 yellowish in colour, and show through the ventral 

 transparent wall of the fresh kidney. The two vessels 

 running to the venae cavae from the venous sinus each 

 give off a small branch to the ventricle near their ventral 

 ends (fig. 5o, Cor.V.). Into the right abdominal vein 

 opens a large vein formed by the union of many branches 

 from the genital gland. Half way along its course this 

 vein receives two lesser vessels from the dorsal region of 

 the visceral envelope, and a branch from the spiral section 

 of the sinus (fig. 53, V.E.V.). 



The Branchial hearts are purplish glandular organs 

 at the base of each gill, into which the lateral venae 

 cavae open, one at each side (PI. VII, figs. 52 and 55). This 

 round opening is guarded by two semi-lunar valves which 

 open into the afferent vessel, and prevent the reflux of 

 blood from the gill (PL VII, fig. 56). The branchial 

 heart is an organ with very thick spongy walls, composed 

 of soft cellular tissue. The central lumen, however, 

 which these walls enclose is very small. On the internal 

 surface of the wall numerous large and small holes may 

 be seen, which lead into short canals (PI. VII, fig. 56), 

 from which other smaller passages lead off, and a third 

 series from the second, and so on, the ultimate apertures 



