Corals. 59 



like transparent flowers. The Sea-pen can move about freely and bur- 

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

 roughly handled, with a greenish light. 



The family of Corticate Corals are well represented in the Aqua- 

 rium. To begin with we have the Black Coral, Antipathies (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 on either side of each 

 branch. In the Bay of Naples there exist white, yellow, and red Sea- 

 fans . the latter being the most numerous. Antipathes 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 entirely carbonate 

 of lime (chalk). 



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

 for ornamental purposes is due to its beautiful colour and to 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 na- 

 ture, 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 freshly fished, 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 placed 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 po- 

 lype, 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 which 

 instrument all imitations can be easily detected. Corals reproduce by 

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

 nies, 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 way 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 fathoms, rare- 

 ty deeper , and is especially obtained on the Ionian Islands and on 

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



