. SEA-FISHERIES LABORATORY. 245 



28). These processes are flattened spatulate or triangular 

 structures fixed by their narrower end to the lip of the 

 nephrostomy In young specimens (up to about 50 mm. 

 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. Each 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). Each of these lobes contains a blind diverticulum 

 of the blood-vessel which traverses the edge of the dorsal 

 lip, hence the processes are bright reel 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 ccelom and ccelomic cells burdened with excretory 

 or with foreign particles. 



The excretory part of the nephridium is a moderate^ 

 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 ccelom. 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. Each bladder opens to the 



