176 PRACTICAL ZOOLOGY. 



The hydroids, jelly-fishes, sea-anemones, and coral 

 polyps, with many other interesting forms, belong to 

 the branch Ccelenterata. The coelenterates are many- 

 celled, radially symmetrical animals, and never pos- 

 sess a digestive tube wholly cut off from the body 

 cavity. 



SPONGES. 



Each pupil should have a small specimen of a commer- 

 cial 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 alco- 

 hol ; a piece of a commercial sponge in alcohol, showing 

 the sponge-flesh still in place ; a silicious sponge ; and 

 elides showing sponge spicules. 



The pupil should make out the following points from 

 his specimen : 



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. 



