SPONGES 133 



sponge to be cultivated are secured, cut into small pieces approximately- 

 one inch square, and fastened either to stakes or to sunken cement 

 plates. From these pieces grow complete sponges which are ready for 

 the market in a few years, the time depending upon the character of the 

 sponge grown and the conditions. When the sponge is gathered, the 

 part that remains after most of it is cut away will continue to grow and 

 develop into another sponge. 



159. Relations to Other Animals. — Sponges are used as food by very 

 few animals, their spicules and the unpleasant character of their excre- 

 tions rendering them objectionable. Because of this fact many other 

 animals take refuge in sponges. The excretions of sponges also play a 

 part in the disintegration of the empty shells of mollusks, the lime of 

 which is thus turned back into the sea water to be used over again by 

 other animals. 



