408 A NATURALIST ON THE "CHALLENGER." 



drug in the market at the time of our visit to Cebu. They were 

 brought off to the ship in washing-baskets full, and sold at two 

 shillings a dozen. 



Mactan Island consists of an old coral reef raised a few feet 

 (eight or ten at most) above the present sea level. At one part 

 of the island, where a convent stands, a low cliff fringes the shore, 

 being the edge of an upper stratum of the upheaved reef, of 

 which the island is composed. This raised reef is here pre- 

 served, but has over the portion of the island, immediately 

 fronting Cebu, been removed by denudation, with the exception 

 of a few isolated pillar-like blocks, which remain, and which are 

 conspicuous from the anchorage. These show that the whole 

 island was once of the same height as the distant cliff. 



Opposite the town of Cebu, the island of Mactan is bordered 

 by a wide belt of denuded coral flat, partly covered at high tide. 

 The surface is scooped out into irregular basins and sharp 

 projecting pinnacles, and covered in all directions with mud, 

 resulting from the denudation. Very few living corals are to be 

 found on these flats, but the flats are fringed at their seaward 

 margin by small beds of living corals. 



These muddy expanses are the haunt of numerous shore 

 birds. In the pools a large Sea- Anemone, of the genus Cerianthus, 

 expands its tentacles in the full blaze of the sun. Cerianthus is a 

 form which uses its "thread cells," which in all its widely varying 

 allies are apparently only employed as offensive stinging organs, 

 to construct a dwelling. The cells are shed out in enormous 

 abundance, and with their protruded filaments matted together, 

 form a tough leathery tube with a smooth and glistening inner 

 surface, which is buried upright in the mud. 



Within this tube the Anemone lives, expanding its tentacles 

 at the mouth of the tube, on a level with the surface of the mud. 

 It has the power of moving itself with extreme rapidity down 

 its tube, and disappears like a flash when alarmed. The species 

 at Mactan Island is very large. The tube measures one foot four 

 inches in length, and is very thick and heavy, though made up 

 almost entirely of thread cells. The animal itself is six inches 

 in length. 



This species of Cerianthus lives in shallow water in the full 



