CORALS AND CORAL-ANIMALS. iqi 



prominent species that belong to this, most numerically abundant, flexible series, reference may 

 be appropriately made to two more abnormal types which, through the possession of hard 

 calcareous coralla, lay claim to a position side by side with the ordinary Madreporaria, as 

 factors in reef-construction. 



The first species of the hard-coralled Alcyonaria that invites attention is the well-known 

 Music- or Organ-pipe coral, Tubipom musica, so called from a fancied resemblance in the arrange- 

 ment of the associated tubes of which its corallum is composed to the pipes of an organ. As 

 a rule, the Organ-pipe coral does not occur in social colonies, the coralla being found, either 

 separately or in small isolated patches, further inshore than the ordinary corals, and most 

 frequently where an accumulation of a certain amount of muddy sediment takes place. An 

 exceptionally rich patch of this highly-characteristic coral is shown in the foreground of Plate 

 XVIII., reproduced from a photographic view taken on the north shore of Thursday Island. Both 

 the corallum and the associated zooids of the Organ-pipe coral are, as shown in Chromo plate 

 X., Figs. 6 to 8, conspicuously coloured. The entire corallum, including the polyp-tubes, and 

 the interconnecting horizontal calcareous laminae, that bind them together at more or less regular 

 intervals, is a bright crimson-red, while the star-like polyps, with their delicately-fringed tentacles, 

 vary in colour from light emerald to a pale sage-green, or sometimes brown. The author was 

 fortunate enough to secure a highly-characteristic photograph of a corallum of this species with 

 a large number of its polyps fully extended. This photograph is reproduced as taken, to the 

 natural size, in Plate XXVI. The species, while commonest in the hotter waters of Torres 

 Strait, is to be obtained throughout the Barrier district. 



The second coral-constructing Alcyonoid type met with on the Barrier Reef bears the popular 

 title of the Blue coral, but is known to biologists under the technical name of Hcliopora ca'riilea. 

 The coralla of this species takes the form of erect clumps, a foot or eighteen inches high, composed 

 of more or less compressed, irregularly lobate, or digitiform, ramifications, which coalesce more or 

 less extensively with one another. The superficial colour of the living corallum in this type 

 is usually a dull bluish-grey ; but the interior, when broken through, is a bright indigo-blue that 

 permanently retains its hue, whence the popular title has been derived. The species is 

 an essentially tropical type, being most abundantly represented in the hotter waters of 

 Torres Strait. 



Until within a comparatively recent date, considerable uncertainty prevailed concern- 

 ing the true zoological affinities of Heliopora. The balance of evidence, submitted chiefly by 

 the American authorities, Agassiz and Dana, was in support of its close relationship to the 

 Hydroid coral-building type Millepora, hereafter described ; and it was left to the late Pro- 

 fessor H. N. Moseley, in connection with the scientific exploration cruise of H.M.S. Challenger, to 

 demonstrate its rightful position among the Alcyonaria. As a matter of fact, this Blue coral is a 

 very difficult form to study, it being so shy of expanding its polyps under artificial conditions, in 



