SOME LOWER ANIMALS 257 



Sponge. A simple study may be made of it. Note how it 

 encrusts plants or rocks, the color, and the rough feeling due 

 to minute needles of silica. The horny or leathery skeleton 

 of the bath sponge is the chief thing to note. The method 

 of fishing for sponges and their preparation are also of 

 interest. 



