ANEMONES AND CORALS 57 



it is called, after a short period settles down and becomes per- 

 manently attached to some substance on the floor of the sea. 

 Developmental changes then take place, leading to the formation 

 of a mouth, stomach, and perigastric cavity ; while the calcare- 

 ous matter gradually deposited by the connective tissue, and 

 forming the stem and spicules, is derived from the products of 

 digestion, for it is from the shells of the minute animals which 

 constitute the food of the polyp that the carbonate of lime for 

 the building up of the Coral stem is chiefly, if not entirely, 

 obtained. 



The Sea-fans have flexible stems enclosed in a soft outer layer, 

 in which the polyps may be embedded or may project as little 

 wart-like growths. Spicules of carbonate of lime are present in the 

 soft parts. The stem is formed of concentric layers of material, 

 which are deposited in the tissues of the deepest portion of 

 the soft parts, one over the other, the outer surface being marked 

 with grooves. They have a wide distribution, and are very beau- 

 tiful objects both in colour and form. 



The handsome, deep purplish-red Organ-pipe Coral (Tubipora 

 musica) is an Alcyonarian which forms very considerable masses, 

 composed of a multitude of small cylindrical tubes placed in 

 rows one over the other, and separated by a kind of semi-tubular 

 and cellular tissue ; it is found in the Red Sea and Pacific Ocean. 

 A living specimen presents a very beautiful appearance, with the 

 little polyps fully expanded, showing their graceful, feathery ten- 

 tacles. If alarmed, the tentacles instantly close, and the polyp 

 withdraws within the tube. Inside the more or less cylindrical 

 tubes there are funnel-shaped projections, and also incomplete 

 horizontal tabulae, but no septa. 



The commonest British Alcyonarian is the so-called " Dead 

 Men's Fingers " (Alcyonium digitattim), which may be found in rock 

 pools exposed at low spring tides, or dredged up from depths 

 of 40 to 50 fathoms. Out of the water it presents an uninviting 

 appearance of a sickly whitish-yellow or pink colour, an ugly mass 

 of slimy-looking substance, shaped like a distorted hand. When 

 the mass is returned to a vessel filled with clear sea-water a trans- 

 formation soon takes place, the surface of the mass becoming 

 covered with large and beautiful polyps. 



The fossil remains of Coelenterates are very numerous and 



