ZOOLOGY. 



close their tentacles according to the fineness of 

 the day. When the feelers are drawn in, the 

 apertures from which they proceed close like the 



Actinia seen from above. Section of Actinia : 



a, cavity of stomach ; b, sur- 

 rounding chambers. 



mouth of a purse, and the animal appears like a 

 simple fleshy tubercle adhering to the rocks. 



ORDER i. Zoantharia. The Zoantharia have 

 the tentacles numerous and simple, while the 

 radiating partitions are in multiples of five or six. 

 They are represented by Actinia or Sea-anemone, 

 many species of which occur along our shores. 

 Some forms, however, are supported by a structure 

 called a coral, which is composed of calcareous 

 matter, or of horny matter, or partly of both. In 

 one group this coral consists of a solid rod or 

 axis, quite smooth on the surface, and presenting 

 no appearance of cups, and merely acting as a 

 support, over which the soft tissues of the animals 

 are stretched. To a coral quite smooth and 

 devoid of cups, the term sclero-basic is applied 

 (Gr. scleros, hard, and basis, pedestal). The 

 Black Coral (Antipathes), which is so much 

 prized, has a sclero-basic coral, composed of 

 horny and calcareous matter, forming a smooth, 

 solid, branching structure, over which the tissues 

 of the animal are stretched. In another group, 

 the tissues of the animal are more or less com- 

 pletely calcified, by the deposition of particles of 

 carbonate of lime in their structure. Such a coral 

 is called a sclero-dermic coral (scleros, hard, and 

 derma, skin), and it can at once be distinguished 

 from the former by the presence of the calcified 

 cups for the polyps. Like the animal which pro- 

 duces it, a sclero- 

 dermic coral may 

 be simple or 

 compound. Thus 

 Carophyllia is a 

 simple coral, and 

 consists of a cal- 

 cified cup or cor- 

 allite. The calci- 

 fied boundary wall 

 of this conical 

 simple corallite is 

 called the theca, 

 the lower part of 

 which is divided 

 by a series of 

 radiating calcified 

 vertical partitions 

 (septa] into chambers or loculi, while the upper 

 part is vacant. Many of these septa run from 

 the interior of the theca, and meet in the centre, 

 forming a cokimella or axial support. 



In a compound coral the various cups are united 

 by calcareous matter, the whole exactly resembling 



Caryophyllia borealis. 



in form the animal which secreted it. As examples 

 of compound sclero-dermic corals may be cited 

 the Brain Corals (Meandrina), and Star Corals 

 (Asteriadce). Amongst simple sclero - dermic 

 corals, the following are found off the coast of 

 Britain in deep water Lophohelia prolifera, 

 Amphihelia ramea, Allopera oculina, and Caryo- 

 phyllia borealis. 



Extensive reefs and many islands in the Pacific 

 Ocean, Indian Sea, and throughout Polynesia, are 

 composed of coral, the product of these minute 

 polypes. Darwin has classified coral reefs into (a) 

 atolls, (b) barrier reefs, and (c) fringing reefs. 



Fringing reefs skirt continents or surround 

 islands. The channel between them and the land 

 is shallow, and outside the. reef there is no great 

 depth of water. 



Barrier reefs may encircle islands or skirt con- 

 tinents. The channel between the land and the 

 reef is navigable, and outside, the soundings in- 

 dicate enormous depths. The reef on the north- 

 east of Australia is 1250 miles long, and from 10 

 to 90 in breadth, and rises from its seaward edge 

 in some places free 1800 feet. 



Atolls are circular coral reefs inclosing an ex- 

 panse of water, which is called a ' lagoon.' The 

 circle has breaks in it here and there, and is 

 generally highest towards the windward side, 

 against which the waves are continually dashing 

 with great violence. The coral-producing polypes 

 cannot exist in fresh water, hence the breaks in the 

 circle where a stream had poured its waters into 

 the ocean ; neither can they exist at a depth of 

 over 80 fathoms, or withstand the heat of the 

 sun's rays. A mean winter temperature of not less 

 than 66 is necessary for their existence. When 

 a reef, by the gradual elevation of the land upon 

 which it is placed, has reached the surface of the 

 water, sand, shells, fragments of coral broken off 

 by the waves, and other substances begin to 

 accumulate, and cocoa-nut trees often grow while 

 the waves still wash their roots. Further accumu- 

 lations from the ocean, with decayed leaves, stems, 

 &c. gradually convert the reef into fertile land. 

 Mr Darwin shewed that a fringing might be con- 

 verted into a barrier reef by the gradual sinking 

 of the land on which the reef is built, the coral 

 polypes gradually building upward; and by a 

 further subsidence, a barrier reef might be con- 

 verted into an atoll. This accounts for the great 

 depth of some of the coral reefs that exist in the 

 Pacific Ocean. 



ORDER 2. Alcyonaria characterised by having 

 the tentacles fringed, and the parts in multiples of 

 four includes Alcyonium, or ' dead-man's fingers,' 



Pennatula. 



so called from its flabby appearance when seen in 

 the fisherman's net It is a composite animal, and 

 is studded all over with little pits, from which 

 polypes protrude. Its body contains a few spicules, 

 and is traversed by a system of canals, which 



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