256 



- KNOWLEDGE ♦ 



[Oct. 26, 1883. 



sea-anemone is termed), is called the cwnosarc, and from 

 this the pretty little polypes bud forth outwardly in all 

 directions. Suppose that the polypes themselves are 

 entirely soft, like ordinary sea-anemones, but that the 

 ca-nosarc, or common basal foot of tlie colony, secretes a 

 horny or calcareous skeleton. It is then evident that if the 

 compound creature is tree-like in form, as it usually is, that 

 a solid axial support would be the result ; and such we find 

 to be the case in the lilack coral {Antipathidiv). 



In another order of corals called the " Asteroid Polypes," 

 or OciocoraUa, the main difference from the foregoing con- 

 sists of the disposition of soft parts in fours and multiples 

 of four, usually eight. And here we have a vast assem- 

 blage of lovely animals both in the flesh and in skeletons. 

 Let us look at some of them. The Sea Pens and Virgu- 

 larias may be seen almost in their vital beauty in Dr. 

 Anton Dohrn's series of museum specimens from the zoo- 

 logical station of Xaples, to which we lately drew special 

 attention. The beautiful red and yellow Gorgonias or Sea 

 Shrubs are well known to every collector of pretty objects 

 of natural history, and are arranged with neat care and 

 precision under many a highly-prized glass-shadeful of 

 lovely objects in the natural history galleries of the 

 East Quadrant. Whilst the valued red coral of com- 

 merce {CoraUium riibrum), in tiaras, necklets, bracelets, 

 and rings, I'c, need not be localised, since they are so 

 attractively displayed that they cannot well be over- 

 looked. All these are called sderohasic or foot^secreted 

 corals, and they all agree in the possession of a solid axial 

 skeleton, to which the polypes themselves do not directly 

 contribute. 



But the case is very different with those other forms of 

 coral called sclerodermic. In these the skeleton or corcdlum 

 is secreted by the polypes, and, therefore, the separate 

 polypes, with their mesenteric septa all calcified, are obvious 

 in the skeleton. Amongst the Hexacoralla several familiar 

 examples of exceptional beauty may be seen in Lady 

 Brassey's case, of which we may particularly mention the 

 large brain corals {Meandrina cerebriformis), and the star 

 corals (Astraa pallida). One or two specimens of the 

 curious fungus coral (Fungia lacerta) which belongs to this 

 group, may also be noted. The Asteroid Polypes or Octo- 

 coralla are represented in Dr. Dohrn's collection Iiy several 

 very line specimens with all their polypes protruded and 

 their tentacles well spread out. The familiar " Dead-men's 

 fingers," which are so commonly -washed on to our sea- 

 shores, and which possess pretty knotted spicules in their 

 tissues, and the red organ-pipe coral {Tuhipora imisicci), 

 which is such a favourite for glass shades, also belong to 

 this group of tissue-secreting corals. 



Lastly, in Lady Brassey's case there are several corals 

 (Distichoporn Brasseyi, Stijlaster sanguinea, tc.) -which 

 were formerly regarded as Actinozoa. But the careful 

 researches of Mr. Moseley, of H.M.'s Challenger, have 

 shown that they are more nearly related to the Hydrozoa ; 

 he therefore placed them in a group by themselves, the 

 Hydrocoralliiue. The life-histories of some of these forms 

 worked out by Mr. Moseley, are pleasingly related by Sir 

 Wy-^-ille Thomson in his volume on the Atlantic. 



Apart from their utility as ornaments, corals are worthy 

 of special notice, inasmuch as they play and have played 

 an important part in the evolution of "the earth's crust. 

 With the single exception of the mollusca, they are perhaps 

 the best guide to the student of stratigraphical geology. 

 The question of the formation and destruction of coral 

 reefs and coral islands which for years puzzled physio- 

 graphists is now a matter which every junior biological 

 student listens to with interest from the professorial orator, 

 as he narrates, step by step, the manner in which those 



structures are reared up and destroyed ; but it required 

 the genius of such men as Darwin and Dana to place these 

 beautifully simple facts into the order of a philosophical 

 problem ; and we cannot do better here than quote the 

 words of Murray, which, as Thomas Carlyle would have 

 said, "puts the whole thing into a nutshell " : — 



" Darwin's theory may be said to rest on two facts — the one physio- 

 logical, and the otlier physical ; the former that those species of 

 corals whose skeletons chiefly make up reefs cannot live in depths 

 greater than from twenty to thirty fathoms ; the latter, that the 

 surface of the earth is continually undergoing slow elevation or 

 subsidence." 



" The corals commence by grcwing up from the shallow waters 

 suiTouuding an island, and form a fringing reef, which is closely 

 attached to the shore. The island slowly sinks, but the corals con- 

 tinually grow upwards, and keep tlie upper sui-face of the reef at a 

 level with the waves of the ocean. When this has gone on for some 

 time, a wide navigable water channel is formed between the reef 

 and the shores of the island, and we have a barrier reef. These 

 processes have but to be continued some stages further, when the 

 island will disappear beneath the ocean, and be replaced by an atoll 

 with its lagoon where the island once stood." 



" According to this simple and beautiful theory, the fringing reef 

 becomes a barrier reef, and the barrier reef an atoll by a continuouB 

 process of development." 



But although Darwin's theory accounts for the forma- 

 tion of these structures adequately, Murray goes on to 

 show in the same paper* that the theory of subsidence and 

 elevation need not be called in at all to account for these 

 phenomena, but that they may arise in the ordinary 

 sequence of events after different modes, and, moreover, 

 that they usually do do so. We cannot here enter into 

 the details of this subject, and must therefore refer the 

 reader to Mr. Murray's paper, which, although strictly 

 scientific, possesses that degree of general interest which a 

 clearly-written article on a novel subject ought to have. 



Finally, those delicate Ccelenterate animals termed 

 Ctenopliora are transparant oceanic creatures, which s-wim 

 about through the agency of ctenophores, or comb-like 

 parallel rows of cilia. And once more shall -ne have to 

 visit Dr. Dohrn's collection to see examples such as Beroe, 

 Ac, perfectly preserved. 



We have neither time nor space to deal -with the 

 Annelids, Crustaceans, or Molluscs, although the last two 

 classes of animals find an important place in the fisheries 

 of the world. We may, however, notice one or two articles 

 of peculiar interest. In the Bahamese section several 

 beautiful pink pearls derived from the large conch-shell 

 may be seen. In Lady Brassey's case and a few other 

 cases in the East Quadrant there are a few Buddha shells. 

 These are the valves of a species of mussel (Anodcmta), 

 into whose substance little models of Buddha are incor- 

 porated ; -whilst the mollusc is j^et alive the models are 

 introduced between its mantle and shell, and in the course 

 of time the former secretes a nacreous coat of mother-of- 

 pearl over the mythical casts. 



We trust our readers will forgive us for the long interval 

 between the first and concluding portions of Professor 

 Cayley's " Philosophy of Mathematics." The laws of space 

 though they may be set aside by mathematicians of the 

 Inconceivable School are unfortunately inexorable towards 

 editors. For a similar reason our discussion of " The Green 

 Sun in India" is delayed for a week. Next week the papers 

 on the " Earth's Rotundity " ^vill be resumed. — Ed. 



* " Proc. Key. Soc. Edin.," Vol. X., 1879-80, p. 505, et seq. 



