The boring animals mentioned as reducing coral stone to mud are very easily found and examined. Almost any old worn piece of coral, and many still living colonies, are found to be studded with small slit-like holes with slightly raised borders. On breaking into the stone each hole is found to lead at once into an oval cavity, say an inch long by three-eighths in diameter, containing a bivalve shell of about the same size, _Lithodomus_ by name, from its appearance known as the “date shell,” which has made the hollow and is continually enlarging it. Other colonies when broken across instead of shewing pure white limestone are found to be honeycombed with yellow or red spongy matter. This is the sponge _Clione_, which has the property, especially astonishing in a sponge, of boring into any limestone, whether coral or shell, making it quite rotten and so, finally, reducing it to mud and sand. Certain worms live in the same way. The largest species of these, by name _Eunice siciliensis_, attains a length of a yard or so, and the thickness of a quarter of an inch, but so intricate is its boring that it is practically impossible to extract a full-grown specimen entire. The head end is at the innermost part of the burrow, and when extracted the two white gouge-like teeth, by which the burrow is cut out, are easily seen. There is a fish too, _Pseudoscarus_ by name, which actually lives on coral! It is commonly taken by fishermen and is easily recognised by its gorgeous green, blue and pink colours, but particularly by its teeth, which are fused into two pairs of chisels, with which the surface of the coral, and with it its living matter, is browsed away. Cut open a specimen of this fish and you find its guts full of fragments of coral[48]. Figs. 66 and 67. Two specimens of _Porites_. In 66 the flesh has been left on the coral and where it is broken it is seen that the dark coloured living matter penetrates the mass only to the bottoms of the coral cups. In this small piece the openings of 14 _Lithodomus_ burrows are seen, and in four of them the lips of the shell are visible. In 67 the base of the still living coral is rotting away, being full of small holes formed by the sponge _Clione_ and small boring worms. Fig. 68. An old piece of coral in which so much of the surface has rotted away that the numerous _Lithodomus_ borings, of which only the small openings can be seen in living corals, are fully exposed. This in spite of partial protection by growth of encrusting stony seaweed as at the point marked _a_. Fig. 69. Section of a large shell, a material very much harder than any coral, yet bored in the same way by both mollusca and sponge. Fig. 70. The mollusc _Pholas_ lying in its burrow in coral. Fig. 70 about natural size, the rest about half this. From specimens in the Cambridge University Museum of Zoology. _Plate XXXI_