WORLD- THO UGHTti. 327 



onoids, which have but eight tentacles, there exists a regu 

 lar gradation of complication which in this place can only 

 be announced. It is a fact of extreme interest, however, 

 that the geological succession of coral animals, so far as we 

 can judge, has been coincident with this structural grada 

 tion. Of fossil Actiniae we can allege nothing, since, hav 

 ing soft bodies, no relics of them could have been preserved 

 if they existed in the early ages of the world s history. 

 But as to the other groups, we find the Fungidce running 

 through the Silurian, Devonian, and Carboniferous ages, 

 while the Porites and Astrceans bedecked the submarine 

 parterres of Mesozoic Time, and the Madrepores united 

 with them to adorn the Tertiary seas, and the Halcyonoids 

 belong to the latest times, 



A farther extraordinary coincidence is furnished by these 

 coral animals. It has been shown by Agassiz, who exam 

 ined the Florida Reef under the auspices of the United 

 States Coast Survey, that the true reef-building polyps ar 

 range themselves along the reef in the order of their rank 

 and successive introduction upon the earth. The Actinice 

 do not appear on the reef for the same reason that they do 

 not figure in the records of geology. They are soft-bodied 

 animals, and never secrete coral. The Fungidce, further 

 more, are not compound animals like the reef-builders, and 

 are not confined to any particular depth in the sea. But 

 when we come to the reefrnaking polyps, we find the true 

 Astrceans at the bottom, followed by the Meandrines, a 

 higher section of the Astrceans. Next, in ascending along 

 the reef we encounter the architecture of the Porites, the 

 Madrepores, and the Halcyonoids in due succession, and 

 presenting a series of conceptions identical with that found 

 in the structural gradation of polypi, and again in the or 

 der of their geological appearance. 



What signify now these repetitions of identical succes- 



