Schematic diagram of a transverse section accross the visceral
mass of L. littorea to illustrate the organisation of the 
central areas of the kidney and the heart. The regions and 
epithelial surfaces of the kidney can be categorised into a
number of structurally different areas and types. These often
have a different ontogenic origin and are specialised to 
perform a number of different functions.

Structures and areas of the kidney and its associated organs:

      a    =   anus
     aa    =   anterior aorta
    aav    =   afferent renal vessel
     au    =   auricle
     bs    =   blood sinus 
     ec    =   extrapallial cavity
      f    =   faecal material 
     kl    =   lumen of kidney sac
     ko    =   kidney nephridial vessel
     pc    =   pallial cavity (mantle cavity)
    prs    =   peri-rectal sinus 
     ps    =   pericardial space 
    rbv    =   renal blood vessel
     rc    =   renopericardial canal 
     ve    =   ventricle


     N.B.  Although this diagram shows the renal epithelium covering
           the nephridial gland, the majority of the nephridial
           gland is in direct communication with the lumen of the
           kidney sac.