624 



THE WONDERS OF GEOLOGY. Lect. VI. 



layer which covers the dark brown coral; some of the 

 polypes are here shown expanded, and others contracted. In 

 this magnified view {PI. VI. Jig. 10) of a single polype, 

 the tentacula are seen expanded, or disposed around the 

 prominent mouth. The appearance of groups of Astreae, 

 and other corals, when viewed while the animals are alive 

 and in activity, is most beautiful ; looking down through 

 the clear sea-water, the surface of the rock appears one 

 living mass, and the congregated polypes present the most 

 diversified and vivid hues. 



The Pavonia are those corals which have deep and iso- 

 lated cells, each containing a large depressed polype, very 

 similar in its appearance and structure to the Actinia. PL 

 VI. Jig. 11, represents a group of cells containing polypes, of 

 the P. lactuca, from the shores of the South Sea islands. 

 The polypes are of a green colour, and there is a connect- 

 ing, transparent, fleshy substance, which extends over the 

 extreme edges of the foliated expansion of this elegant 

 zoophyte. 



From the magnitude and muscularity of the polypes in 

 these large lithophytes, and the increased number and 

 strength of their prehensile organs, they are capable of seiz- 

 ing and digesting more highly organized prey, than the 

 delicate, minute, cellular zoophytes. 



25. Meandrina cerebriformis ; or Brain-coral. — The 

 large hemispherical corals, having the surface covered with 

 meandering ridges and depressions, disposed in a manner 

 somewhat resembling the convolutions of the brain, are 

 well known by the name of Brain-stone {Lign. 138). In 

 a living state the mass is invested with a fleshy substance, 

 variously coloured, and having numerous, short, conical, 

 polypiform, confluent cells, arranged in rows between the 

 ridges. This zoophyte sometimes attains considerable mag- 

 nitude ; a very beautiful specimen in the British Museum is 

 four feet in circumference. The base of the Meandrina, 



