26o L(i:LEXTliKAl KS: I'ULVPS. 



In the true Madrepores, Figure 500, the Pol}'ps do not 

 secrete coral at the base ; hence the cells of the coral 

 are very deep, and these corals spread and branch into 

 the most beautiful and varied forms, and the Polyp at 

 the end of a branch. Figure 500, is always larger than 

 the others. 



In the great group of the Astrsans the tentacles 

 occur in multiples of six. Those of this group, called 

 Brain Corals, or Meandrinas, ha\-e the surface covered 

 with winding trenches. Figure 505, on each side of 

 which there is a row of tentacles. The form of the 

 Meandrinas is generally that of a hemisphere, and 

 some of these masses are twelve feet in diameter. 

 The true Astra;ans, or Star Corals, Figure 507, have 

 the cells in the form of concave pits, and the common 

 forms of this coral are hemispherical or dome-shaped 

 masses, some of which are twenty feet in diameter ; 

 the Polyps themselves are often an inch in diam- 

 eter. Most of them, however, are veiy much smaller. 

 One beautiful little Astrjean, Dana's Astrangia, has its 

 home in Long Island Sound, where it occurs in little 

 clusters upon the stones and shells, from just below 

 low-water mark even down to ten fathoms in depth. 

 It thrives well in the aquarium, and eats little mol- 

 lusks and other small animals with a good relish. In 

 those Coral Polyps called Oculinas, the coral, when 

 young, spreads so as to form a broad base ; later, beau- 

 tiful tufts and treelike branches arise from this base. 

 A portion of one of these Oculinas is shown in Figure 

 509. 



In the great group of Fungus Corals, the coral is 

 broad and flat, looking like a toadstool without a 

 stem, as in Figure 510. Polyps of this kind have 



