106 THE SEA MUSHROOM. 



down and accumulates in their interstices. Being 

 free, they merely repose on the sand at the bottom of 

 the water. Their power of locomotion is very limited. 



The sea mushroom might, however, be easily 

 supposed liable to danger : a violent agitation of the 

 water, for example, might reverse it ; and how then, 

 it might be asked, shall it regain its position ? The 

 Creator has provided for the well-being of this, as well 

 as every other creature. The living jelly that covers 

 its surface, is so endowed as to secrete within its sub- 

 stance little bubbles of air ; these act as floats, and 

 thus the lighter side is kept uppermost on the waters. 



In the animal just referred to, we observe a single 

 polyp covered with gelatine, but in other instances 

 a gelatinous expansion appears common to many 

 associated polyps. The difference is here apparent 

 between a house with a solitary inhabitant, and a 

 large number of persons dwelling under the same 

 roof, which the engraving will illustrate. A similar 



SPECIES OF MADREPORE. 



instance appears in the red coral of commerce : it is 

 a branching calcareous tree, secreted by the gelatine, 

 which spreads round it like a rind; while the various 



