165 
28). These processes are flattened spatulate or triangular 
structures fixed by their narrower end to the lp of the 
nephrostome. In young specimens (up to about 50 mim. 
long) these processes are represented by small ciliated 
tubercles on the edge of the lip (fig. 25), but later these 
not only increase in number but become larger and sub- 
divided distally. Hach of the processes eventually forms 
a flattened structure the edge of which is sub-divided by 
deep notches into from two to fourteen rounded lobes (fig. 
29). Mach of these lobes contains a blind diverticulum 
of the blood-vessel which traverses the edge of the dorsal 
lip, hence the processes are bright red in colour. — ‘The 
edges of both the dorsal and ventral lips are richly ciliated, 
and there are also numerous long cilia within the mouth 
of the funnel the motion of which is very obvious in fresh 
nephridia examined on a slide in sea water. ‘The action 
of these cilia creates a current passing down the funnel 
to the oval aperture which leads into the middle or ex- 
cretory part of the organ. ‘This current carries into the 
nephridium small particles of foreign matter introduced 
into the coelom and coelomic cells burdened with excretory 
or with foreign particles. 
The excretory part of the nephridium is a moderately 
thin-walled sac, usually dark brown, sometimes almost 
black in colour, owing to the presence of large numbers of 
brown excretory granules in the cells lining the sac. 
These excretory products are doubtless derived from two 
sources from the blood flowing through the network of 
vessels upon the sac and from effete materials carried into 
the nephridium from the ceelom. This portion of the 
nephridium tapers posteriorly and opens into the bladder, 
which is usually greyish or brownish in colour. When 
expanded the bladder is more or less spherical, but when 
contracted it is rosette-like. Mach bladder opens to the 
