SPONGES. 



A. A CALCAREOUS SPONGE (Grantia). 



Notice the shape. Is the surface smooth? How many 

 openings do you find? What differences do you find 

 between the ends? Split the sponge lengthwise with a 

 sharp scalpel, laying open the central cavity (cloaca). 

 Where is the large opening (ostium) by means of which the 

 cloaca is connected with the exterior? By what is it sur- 

 rounded? In the walls of the cloaca notice the openings 

 (excurrent canals) best seen after the sponge has dried. 

 In the cut walls see the small chambers (ampullce). Draw 

 one half of the sponge, naming the parts. Cut the other 

 half of the sponge transversely and notice the radially 

 arranged ampullae. Place a bit of the sponge in weak 

 hydrochloric acid. What occurs? Boil another bit in 

 caustic potash (a few drops of a 5% solution), then place 

 the fluid on a slide ; examine under the microscope. Draw 

 the spicules which you see. Crush a dry bit of the sponge 

 in the fingers. Has it any elasticity? 



B. A BATH SPONGE (Spongia). 



Select small rounded sponges for this purpose. Notice 

 the irregularity of the surface. Do you find any large open- 

 ing in any way comparable to the ostium of the calcareous 



sponge? If so, split the sponge through this opening and 



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