26 INTRODUCTION TO ZOOLOGY. 



2d, That in the Pacific and Indian oceans are tracts where 

 a gradual subsidence of the bottom of the sea is going on; and 



3d, That the Polypes work most efficiently at the outer 

 edge of the reef, where the water is the purest and best aerated, 

 and where their food is most abundant. 



To enter into further details upon this subject would here 

 be out of place. But this brief notice of the labours of Coral- 

 building Polypes cannot receive a more appropriate close than 

 that which has been furnished by the poet: 



" Millions of millions thus, from age to age, 

 With simplest skill and toil unweariable, 

 No moment and no movement unimproved, 

 Laid line on line, on terrace terrace spread, 

 To swell the heightening, brightening, gradual mound, 

 By marvellous structure climbing tow'rd the day. 

 Each wrought alone, yet all together wrought. 

 Unconscious, not unworthy instruments, 

 By which a hand invisible was rearing 

 A new creation in the secret deep. 

 Omnipotence wrought in them, with them, by them ; 

 Hence what Omnipotence alone could do 

 Worms did. I saw the living pile ascend, 

 The mausoleum of its architects, 

 Still dying upwards as their labours closed : 

 Slime the material, but the slime was turned 

 To adamant by their petrific touch ; 

 Frail were their frames, ephemeral their lives, 

 Their masonry imperishable." MONTGOMERY'S PELICAN ISLAND. 



polypes began originally to build at moderate depths, and the foundations 

 of their structure were gradually carried downwards by the prolonged 

 subsidence of the bottom of the sea, it is obvious, from his statements, 

 that the ceaseless labours of the polypes are capable, in the lapse of time, 

 of producing all the phenomena described. Fide Darwin's interesting 

 work on the Structure and Distribution of Coral Keefs, and an able 

 analysis of his theory in Lyell's Principles of Geology, vol. iii. 



Fig. 14. SEA ANNKMONE. 



