56 ANEMONES AND CORALS 



The Sea-pens are free-swimming, more or less pen-shaped 

 Alcyonarians, with a wide geographical range, and living at vari- 

 ous depths of the ocean, some being quite shallow-water forms, 

 others living at a depth of some three hundred fathoms. 1 Many 

 are highly phosphorescent, and they are often brilliant in colour. 

 Some live with their slender pointed root in the sand, but they are 

 not fixed to any base. Their surface is soft, and may have three 

 kinds of polyps upon it. The central stem is composed of horny 

 and calcareous matter, traversed by bands of soft tissue, the 

 ectoderm usually containing calcareous spicules, often very beau- 

 tiful in colour and form. 



The handsome Red Coral (Corallium rubrum), the hard cleaned 

 stem of which is familiar as an ornament, is an Alcyonarian which 

 lives attached to rocks and other substances on the floor of the 

 sea in the Mediterranean, and in parts of the Atlantic and Pacific 

 Oceans. Off the coast of Algeria, the east coast of Spain, and the 

 coasts of Italy and Sicily there is an important Coral fishery, in 

 which some six hundred or more small boats, fitted with a rude 

 dredging apparatus for breaking off and bringing up the Coral, 

 are employed. 



If a portion of the red stem of the Coral be examined, delicate 

 striations will be noticed upon it, and a section will show a con- 

 centric arrangement of calcareous material tinted with delicate 

 shades of red. The polyps form this stem by the deposition of 

 the calcareous grains in a connective tissue, the whole being 

 covered with a somewhat dense soft part, in which there are 

 canals or water systems running over the hard stem. The polyps 

 are large and handsome, crowned by eight feathery tentacles, and 

 having a thick base. A mass of spicules surrounds the hard stem, 

 and becomes gradually connected to form the outer layer. The 

 colony increases by budding or gemmation, a process which leads 

 to an increase in the number of polyps forming a colony, but not, 

 so far as observed, to an increase in the number of colonies. 

 Sperms and ova are formed in separate individual polyps, sexual 

 reproduction occurring usually about once a year. The ova are 

 probably fertilised after their discharge from the parent's mouth, 

 and become ciliated. The free-swimming larva, or planula, as 



1 During the Challenger Expedition, specimens were dredged up from 1,200 to 

 2,125 fathoms. 





