Corals. 59 



like transparent flowers. Tiie Sea-pen can move abont freely and bur- 

 row deep into the sand with its stalk. At night it phosphoresces, when 

 handled roug-hly, with a greenish lig-ht. 



Tlu' family of Corticate Corals are well represented in the Aqua- 

 rium. To begin with wo have the Black Coral , Antipathes (Fig-. 107) , 

 and the Sea-fan, Gorgonia (Fig-. 105), possessing skeletons which consist 

 of a horny substance. The branches of Gorgonia all lie in one plane , 

 and when the polypes protrude their bodies and expand their ten- 

 tacles, they project like small feathery flowers ou either side of each 

 branch. In the Bay of IS'aples there exist white , yellow , and red Sea- 

 fans , the last being the most numerous. Antipatlies has a glossy black 

 skeleton, which attains in large specimens the thickness of a finger; it 

 is used, although rarely , as the so-called black coral for ornamental 

 purposes. The skeleton of the White Coral, Isis (Fig. 104), consists of 

 alternating pieces of horny and calcareous matter ; in the Red Coral 

 which belongs to the same family , the skeleton is composed entirely of 

 carbonate of lime or chalk. 



The great value of the Red Coral , Corallium rubrum (Fig. 106) , 

 for ornamental purposes is due to its beautiful colour, and the hard 

 texture of its skeleton, enabling it to take a high polish. The ancients 

 valued corals greatly, but they had a wholly erroneous idea of their nat- 

 ure , an idea shared even now by many people ; they considered the 

 Coral to be a plant, which remained soft while in the sea , but which 

 became hard suddenly on being taken out of the water. But if a 

 branch be examined, as soon as it has been fished from the sea, it will be 

 found to be enveloped by a coating , also of red colour , just as the 

 wood of a tree is enveloped by its bark. Such a branch replaced care- 

 fully in a large vessel of fresh sea-water will after a short time shew 

 at numerous points of its surface the expanded coral-animals, each with 

 its eight feathery tentacles. Each individual has the structure of a pol- 

 ype , as described above , and is organically connected with all the 

 others by means of canals, which transmit food from one living polype 

 to the other. In the covering , besides these canals , are numerous 

 microscopic spindle-shaped particles of carbonate of lime ; the axis is 

 formed by a fusion of such particles. This structure of the coral is 

 very readily distinguished under the microscope , by the aid of Avhich 

 instrument all imitations can be easily detected. — Corals reproduce by 

 means of eggs or by buds. There exist separate male and female col- 

 onies, besides those which bear both sexes; sometimes, too, hermaphro- 

 dite polypes (individuals with male and female reproductive organs) are 

 found. The egg develops within the maternal polype into a pear-shaped 

 being, which makes its Avay out through the mouth of the mother-polype 

 and swims about freely for some time ; after this it fixes itself with one 

 end and becomes transformed into a polype, which forms new individuals 

 by budding and thus gives rise to a new colony. 



The Red Coral is a gift of the Mediterranean. Here it grows on 

 rocky banks near the coast at a depth of from -40 to 100 fatlioms , rare- 

 ly deeper , and i.s especially obtained on the Ionian Islands and on 

 the coasts of Algiers and Tunis ; the last named place alone yielding 



