16 PORIFERA. 



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

 small pores, jyrosopyles, 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 moderately 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 

 fiagella. Are flagella in all of the canals? In favorable situa- 

 tions it can be easily seen that the cells that have flagella possess 

 collars also. (Collars may be withdrawn by cells so they pro- 

 trude but slightly.) You see now what causes the current of 

 water. Do you understand how a sponge feeds ? Compare the, 

 choanocytes of the sponge with choanoflagellate protozoans. 



Make a drawing showing the arrangement of choanocytes. 

 Examine transverse sections of a specimen that has been 

 decalcified and stained. 



1. The cloacal chamber is lined by a pavement of epithelium. 



2. The radial canals are lined by more conspicuous cells, 

 the gastral epithelium, or choanocytes. 



