CHAPTER XVI. 

 PORIFERA. 



SPONGES. 



EACH pupil should have a small specimen of a commercial 

 sponge, showing large holes at the top, but not with large holes 

 running straight through. 



The teacher will need several specimens of larger sponges ; 

 one of the simple calcareous sponges, in alcohol ; a piece of 

 commercial sponge in alcohol, showing the sponge flesh still in 

 place ; a siliceous sponge ; and slides showing sponge spicules. 



The pupil should make out the following points from his 

 specimen of common sponge : 



1 . Its elasticity ; test first the specimen dry, and again after 

 wetting it. Compare the elasticity of different kinds of sponges. 



2 . The fibrous structure ; with forceps tear off a bit of the 

 sponge and examine with a lens. Then examine under the 

 microscope. 



3. The sponge was attached by its basal surface to rock. 

 Find where it has been trimmed away with shears ; perhaps if 

 this has not been thoroughly done, some bits of rock may be 

 found clinging to the base. 



4. Examine now the different channels by which the sponge 

 is perforated. 



a. Large, craterlike tubes, opening at the top of the sponge. 

 Looking into these, it may be seen that they give off branches. 

 If you can see right through the sponge by looking into these 

 openings, you may know that too much of the base has been cut 

 away, and your specimen is not a good one. With a razor or 



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