SPONGES. 131 



study the section. Can you find canals branching from the 

 ostium? If so, sketch their arrangement. 



Crush a bit of the dry sponge between the fingers. How 

 does it compare with the other form? Examine a very thin 

 bit of it under the microscope; can you find spicules? 



It is to be noted that in the bath sponge of commerce 

 only the hard or skeletal parts are present, the flesh having 

 been washed away. In the calcareous sponge, as put up 

 for laboratory use, flesh and skeleton are both present. 



Read the section on sponges (pp. 158 to 161). 



