38 PORIFERA 



embedded in the walls of the sponge, will be seen opening 

 into the cloaca. Are the apopyles arranged in any order? 



5. With the low power of your microscope (with the light 

 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 occasionally 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 par- 

 ticles are moving in a definite direction near the general sur- 

 face and near the osculum. • 



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



