22 SPONGES 



goes into the secondary incurrent canals and through the prosopyles into the 

 secondary radial canals ; from these it passes by the apopyles into the primary 



Prosopyle 



Badiating Chamber 



Pore or Ostium 



Inhalent Canal 



Fio. 7. — Transverse Section of a Syoon Sponge. The central space is the 

 gaatral cavity. From Masterman's Text-book of Zoology. 



radial canals, and so into the gastral or paragastric cavity. Example 

 Lexidlla (Class, Calcarea ; Order, Heterocoela). 



Primary Radial Canal 



-Primary Inhalent Canal 



^Secondary Inhalen Canal 



\.^ Secondary Radial Canal 

 or Radiating Chamber 



Fi(i. 8. — Transverse Section of a part of the wall of a Leucon Sponge. 

 From Masterman's Text-book of Zoology. 



4. The Rhagon Type. 



This type resembles the last one and can be derived from it. Here the 

 primary incurrent canal communicates by the prosopyle with the secondary 

 radial canals, which take on a rounded shape and are lined by choanocytes. 



