GRANTIA. 21 



turned off) examine the cut wall and find that it is traversed by 

 parallel tubes. Determine that these tubes are of two kinds. 



(a) Regular, nearly cylindrical tubes that open into the 

 cloaca through the apopyles and that bear tufts of spicules on 

 their closed ends, at the surface of the body. These are the 

 radial canals. It is frequently hard to see their openings into 

 the cloaca, as the apopyles are narrow, so the section only occa- 

 sionally passes through them. 



(6) Smaller and less regular tubes that open on the outer 

 surface between the clusters of spicules, and do not open into 

 the cloaca. These are the incurrent canals. In life there are 

 small pores, prosopyles, that open from the incurrent canals 

 into the radial canals. These openings are very minute and are 

 apparently capable of being closed. They are never visible 

 in dried material. 



6. Examine thin, transverse sections of a dry sponge and 

 determine the positions of radial and incurrent canals. 



Make a drawing that will show the arrangement of the canals. 



7. Examine the spicules and determine their positions as 

 regards canals. Boil a portion of a sponge in caustic potash 

 until only the spicules remain and examine the spicules. See if 

 more than one kind occurs. 



Draw specimens of the spicules. 



Living and sectioned material. 



1. Place a living sponge in a watch-glass of sea-water, add a 

 little powdered carmine, and examine it with the low power of 

 your microscope for currents of water. See if particles are mov- 

 ing in a definite direction near the general surface and near the 

 osculum. 



2. With a sharp razor cut tangential sections of the wall, 

 as thin as possible, mount in sea-water under a cover, and 

 examine with a low power. This will show both incurrent and 

 radial canals in cross-section. How can you distinguish one 

 from the other? In a favorable place look for moving flagella. 

 Are flagella in all of the canals ? In favorable situations it 



