Coral Insects and Coral Islands—Polynesia—Operations of the Coral Insect—Growth of Coral Reefs.  
Many of the large and beautiful islands that stud the Pacific Ocean, like emeralds in a field of blue, are artificial; that is to say, they were made by artists—they were actually built by artisans!
 
These artisans are the coral insects; and as they not only affect the face of the sea by raising large islands above it, but also, in consequence of their labours, assist in causing the circulation of the ocean, we think they are justly entitled to very special attention.
 
The great archipelago called Polynesia covers an area of the Pacific nearly 5000 miles in length, and not far short of 2000 in breadth. Some of the islands of this group are of volcanic origin, and some are crystal; but by far the greater number are of coral formation—the work of those curious little insects, which are so small that they inhabit a dwelling sometimes little larger than a pin-point.
 
The manner in which these islands are made is, to some extent, a matter of uncertainty. The most generally received opinion is, that the insects fasten round the summit of a submarine mountain, and build upwards until they reach the surface of the sea, where they die, and their labours cease. As, however, the sea is sometimes unfathomable close to those islands, it has been supposed that the submarine islands on which the corallines began to build have gradually subsided, and that, as they did so, the insects always built a little more, so as to keep the top of their structures on a level with the sea. Above the sea they cannot build. To be washed by the waves is essential to their existence.
 
We do not think this a very satisfactory theory, because it supposes a prolonged subsiding of these islands, and then an unaccountably sudden stoppage. For although the corallines might continue to build during the whole time of subsidence, it were utterly impossible that the coral island, with its luxuriant herbage, could be formed until that subsidence should have ceased. The manner in which the islands are formed makes this obvious.
 
When the coral reef, as it is called, reaches the surface, it advances no further. Soon the action of the waves breaks off the branches of the upper portions of coral, which are tossed upon the reef, and pulverised into fine sand. This goes on increasing until the island rises a little above the waves.
 
When this happens, birds alight there; sea-drift is carried thither; seeds are blown to it by the wind; and gradually a few green blades arise. From this little beginning it is easy to conceive the process by which at last a flourishing island springs up. At the same time, it is not easy to see how such islands could ever be formed on the supposition that the submarine rocks on which they were founded were perpetually subsiding.
 
But be that as it may, we have no difficulty in understanding the fact that the coral insect does build those islands. It possesses the power of secreting the lime held in solution by sea water, and depositing the same on the rocks below the waves. The coral rock is the edifice of the coralline. The insect itself is a soft and very minute worm, which, when washed by the waves, thrusts its head out of its tiny little door, and spreading abroad its numerous feelers, so that it resembles a beautiful little star, moves these about as if enjoying itself—though, doubtless, it is actually engaged in the process of manufacturing its little atom of coral rock.
 
It is extremely interesting to think of the immense power of union thus exhibited. Singly, those little creatures could not produce a sufficient result to attract the attention of any creature save such as chanced to come in direct and close contact with its little cell. United, they have formed vast islands, which have become the ab............