IV PORIFERA 59 



3. Treat a small piece of various common sponges with nitric 

 acid ; this will destroy the organic matter, leaving a sediment of 

 siliceous spicules, which after careful washing should be examined 

 under the microscope, and the kind of spicule characteristic of the 

 different sponges noted. 



4. Examine the collection of sponges in the nearest Natural 

 History Museum. 



