224 THE AHIMAL KINGDOM. 



form for themselves a permanent attachment which prevents 

 their being tossed about by every wave of the element in which 

 they live. The stony substances so formed are called corals, 

 and their mode of formation causes them exactly to repre- 

 sent the animal which secretes them. The upper surface is 

 always furnished with radiating plates, the remains of the 

 calcareous particles which are deposited in the longitudinal 

 folds of the stomach. These, in all probability were the 



FIG. 8. TUBIPORA MTJSICA. 



constructors of all the strata of limestone rocks, which 

 form some of our largest mountains they were once the 

 beds of seas, and were up-heaved by internal forces. The 

 Madrepores (fig. 9) are also of this order, and form the 

 stony matter in the same way. These are of various pat- 

 terns, and the beautiful brain-stones in the British Museum 

 are of their construction." 



The fourth order of Zoophytes are the Ascidioida, including 



