30 STRUCTURAL AND SYSTEMATIC ZOOLOGY 



for in clear water attached to submerged branches, logs, 

 and rocks, and especially on the timbers of dams and 

 mill races. In purchasing toilet sponges for specimens, 

 care should be taken to select some which show single, 

 others numerous, openings and canals, while still others 

 should have particles of sand and of shells embedded in 

 the lower part. 



Using Grantia as a type of the simple sponge, study 

 its shape, color, and mode of attachment; the large 

 opening (osculum) at the upper end surrounded with a 

 row of spicules. Note the small openings, inhalant pores, 

 on the surface. Cut the sponge open longitudinally and 

 note the pores opening into the central cavity. These 

 pores will be seen to be the ends of canals which run 

 horizontally outward. They do not, however, open to 

 the outer surface. These are the radial canals. Lying 

 between two adjacent radial canals will be found an 

 incurrent canal, the outer opening of which is on the 

 outer surface of the sponge. This canal has no opening 

 directly into the central cavity. Water carrying food 

 particles is drawn into the incurrent canals and passes 

 into the radial canals through pores in the walls of 

 tissue between the two canals. It then passes out of the 

 pores at the inner ends of the radial canals, into the larger 

 central cavity, and out through the osculum. The flow 

 of water is produced by the action of ciliated cells which 

 line the radial canals (Figs. 13, 14). 



Microscopic sections will show the arrangement of the 

 canals and of the spicules of lime in the tissue of the 

 sponge, as well as the arrangement of the cellular parts 

 of the body. Large amoeboid cells (ova) are frequently 

 found in the walls between the canals. The spicules 

 may be obtained free from adhering tissue by boiling a 

 fragment of Grantia in caustic potash in a test tube. 

 As the spicules do not dissolve, the fluid may be drained 



