3474 



CCELENTERA TES 



of a branch; the illustration of Caulastrcza showing an example of this. It will be 

 understood from this description that only the layer of* growing polyps with their 

 intercommunications can be spoken of as living; and as this layer rises higher and 

 higher by secreting fresh layers of carbonate of lime, the living linings of the com- 

 municating canals are either withdrawn or die away, and all beneath the living 

 layer is mere dead matter built up and left behind by the coral animals. 



Before passing to our survey of the corals themselves, two other points deserve 

 attention. Not all corals form stocks. Some remain single, like the mushroom 

 corals (Fungidce}, which grow to a very large size with a heavy solid skeleton; and al- 

 though these form new polyps by budding, the latter become detached and live 

 as solitary individuals. Again, although coral reefs are due to the great power of 

 multiplying by division or budding, yet all corals, so far as is known, also at certain 

 times produce eggs. The further development of these eggs gives rise ultimately 

 to a small polyp, which settles down and commences to secrete its pedestal and then 

 to bud, thus starting a new coral stock. 



SIX-RAYED POLYPS Order HEXACTINIA 



This name must not be taken too strictly. It is true that it was applied in 

 good faith, because it was believed that this order always had exactly six or 

 some multiple of six as the number of the tentacles; but corals are tied by no 

 such rigid rules, and all we can say is, that the number of tentacles in this 

 order generally approximates to some multiple of six. Among the Hexactinia 

 the sea anemones take the first place. They spread over all seas, being 

 especially plentiful in the temperate zones, near the coast, at depths which 

 bring them within the reach of every observer. They are distinguished by their 

 solitary manner of life, their size, and their vivid and usually beautiful coloring. 

 The skin is firm and leathery, and often covered with warts. It does not secrete 



any calcareous skeleton either inside or 

 outside, so that the animal is soft and 

 capable of great contraction and changes 

 of shape. Most sea anemones use the 

 basal disc for attachment, and can move 

 from place to place by means of it, but 

 a few species bore into sand with the 

 posterior end of the body, or else secrete 

 or build a sheath which they inhabit. 

 In our colored plate are depicted, in 

 their natural brilliant colors, a number 

 of sea anemones living in the Naples 

 aquarium. To the left, in the fore- 

 ground, are two examples, one extended 

 and the other contracted, of the red 

 Actinia equina, which varies greatly 

 OK SEA ANEMONE (magnified). in color. In the centre of the group, 



