532 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
Kledone, and communicates with the exterior directly by 
means of the genital ducts and indirectly by means of the 
so-called ‘* Water Vascular Canals.” These are two long 
slender ducts leading from the genital gland into the 
pericardium. The right duct is partly shown (fig. 40, 
W.V.C.) where the canal runs dorsal to the right kidney 
and pericardium, and opens into the latter dorsally, just 
behind the reno-pericardial opening. In the female there 
are two symmetrical canals which are long, slender and 
thick-walled, and open posteriorly into the genital capsule 
(Pl. V, fig. 89, W.V.C. and ap. wt.) These internal 
apertures are just exterior to the internal apertures of the 
oviduct (fig. 39, 2. od. ap. int.). In the male, however, 
the right canal alone resembles that of the female in width 
and position, while the left is much wider—particularly 
in the region near the genital gland—and opens into the 
genital capsule quite anteriorly (Text fig. VII, A.p. 90). 
In both sexes the pericardial pouches and the water canals 
are lined by ciliated epithelium, and as shown (PI. VI, 
fig. 51), the water canal follows the course of the sexual 
duct for the greater part of its length. 
EXCRETORY SYSTEM. 
The Kidneys—a single pair of large transparent sacs 
—-are exposed by stripping off the epithelium which covers 
the visceral mass. They lie on the postero-ventral surface 
of the visceral mass, ventral to the heart and posterior 
to the greater part of the alimentary canal (Pl. V, fig. 37, 
R.K.). The left kidney stretches a little further forward 
than the right. In young females these sacs may cover 
the whole postero-ventral surface of the body, but in older 
females and all males the genital gland pushes them 
anteriorly and laterally, by its ventral protrusion (fig. 37, 
