CHAPTER II 

 PORIFERA 



The porifera or sponges are plant-like aquatic animals, all but one 

 family of which are marine. 



The typical or primary form of a sponge is cylindrical or vase 

 shaped, Fig. 7, but in nearly all cases a process of branching has con- 

 verted the simple vase into a highly complex organism or colony. 

 In the simple sponge the central cavity opens to the exterior by a 



PIG. 7. A colony of simple sponges. X/- 



single, large, excurrent opening or osculum, and by numerous minute 

 inhalent openings or pores, Fig. 7. The pores lead into more or less 

 complicated systems of canals which are lined with vibrating flagella 

 that cause currents of water to flow through the canals into the central 

 cavity and thence out of the osculum. It is these currents of water 

 that supply the organism with food and oxygen, and at the same time 



