CHAPTER XIV 

 PHYLUM PORIFERA SPONGES 



Porifera means " pore-bearers, " and the sponges could 

 not have been better named. The body of any sort of a 

 sponge is full of little canals which open through minute 

 apertures over the whole outside surface (Fig. 65). On 

 the interior the canals connect with larger channels which 



A B 



FIG. 65. Structure of a simple sponge. A, half of an animal split length- 

 wise to show the central longitudinal canal and the lateral canals (p) leading into 

 it. B, enlarged section of a sponge's body wall showing different types of cells; 

 a, amoebocyte; 6, undifferentiated cell; c, collared flagellate cell, or choanocyte; 

 e, epidermis on outside of body; s, spicule within the cell that formed it. 



lead again to the outside. Certain portions of the internal 

 canals are lined with peculiar cells, the choanocytes, which 

 each bear a flagellum and a flexible collar surrounding it 

 (B, c). The flagella on all of these cells wave constantly 

 and create currents in the canals. Most sponges have a 



157 



