DEVELOPMENT OF NEPHRIDIA OF PHERETIMA 



73 



after being opened from the ventral and not the dorsal 

 side. 



As the nephridial mass grows in size we can soon distinguish 

 the two ends of the growing nephridium, as shown in Text- 

 fig. 6. One end grows inwards along the septum towards the 

 dorsal vessel, beneath which it meets its fellow of the other 



Portion of the whole mount of an embryo 8 mm. in length, showing 

 the rudiments of the septal nephridia on each side of the dorsal 

 blood-vessel, d.v., dorsal blood-vessel, double behind ; i.n., 

 integumentary nephridia ; s.7i., septal nephridia ; i.s., inter- 

 segmental septa. 



side to form the supra-intestinal excretory duct ; we can call 

 this end the centripetal end. The other end of the nephridial 

 rudiment at this stage is away from the dorsal vessel, and 

 prohferates to form a mass of cells which project in front of 

 the septum to form the beginnings of the ' funnel ' of the 

 nephridium. This pre-septal portion of the nephridium soon 

 attains to a considerable size, and is a prominent feature of the 



