THE PHYSIOLOGY OF EXCRETION. 91 



parts: the crown (K), which is formed by a number of ciliated 

 cells, and the receptaculum (R), a cavity which is surrounded 

 by a wall of connective tissue and possesses only one opening 

 towards the point of attachment of the ciliated crown cells. 

 This opening is the place where the excretory granules are 

 drawn into the receptaculum. The nephridium consists of a 



Fro. 3. 



row of cells which extends from the receptaculum to the 

 nephridiopore (np} or the terminal vesicle (E). This is all we 

 need to know for the moment (Fig. 3). 



The next question is: How do the excretory granules get into 

 the funnel cavity? 



I have already mentioned that a current is produced by the 

 cilia which line the free surface of the funnel cells, by which 

 current the remains of the excretophores are drawn into the 

 funnel cavity. I have now to add to this a theory of ciliary 

 motion, which is based upon structural evidence. From the 

 surface of a ciliated cell and slightly inclined to the same arise 

 a great number of parallel straight rods, which stain intensely 



