154 THE GREAT BARRIER REEF. 



on this branch of biology. The suggestion offered in some quarters that it might not im- 

 probably be a worm-tube parasitically encrusted with a typical Zoanthus presented itself to 

 the author's mind on first obtaining specimens at Port Darwin, in the year 1888. Several 

 facts, however, militate against the acceptance of such an interpretation, which, if adopted, 

 would involve the improvisation of a far more abnormally constituted worm than zoophyte. 

 Although sought for diligently, no examples, either living or dead, or at any younger or more 

 advanced stage of growth, could be discovered, in which the top or distal end of the tube 

 was open, as obtains with the dwelling-tubes of all known tubicolous annelids, of which such 

 genera as Sabella and Chaetopterus may be cited as characteristic types. In all known worm- 

 tubes, moreover, the lumen of the tube is smooth and cylindrical throughout, and does not 

 deviate into zigzag angles or irregularly protruding nodes, of from two to three on the 

 same horizontal plane, as obtains in the Zoanthus-associated structure. If, again, as suggested 

 with reference to the simplest zigzag tubes, such zigzag line of growth had been induced 

 by the Zoanthus repeatedly interfering with the worm and causing it to deviate from its 

 normal rectilinear growth to alternate sides, worm-tubes of normal construction, either partly or 

 wholly free from invasion by the supposed parasitic Zoanthus, should most assuredly have been 

 found. One other detail of suggestive significance remains to be recorded. It is a distinctive 

 feature of these Zoantharian associated tubes, that, as illustrated in the accompanj'ing figure, their 

 proximal or attached ends spread out to a greater width than the erect tube, after the manner of 

 the attached base of a Gorgonia or other compound Actinozoarian. In the case of a fixed worm- 

 tube, on the other hand, the tube is always smallest at its proximal or attached end, since it 

 represents at that point the dwelling-house of the worm in its most juvenile tubicolous stage 

 of development. 



It may be remarked of the dried, somewhat eroded, example, photographically delineated 

 in the accompanying figure, that while the base exhibits its characteristic expanded form, the 

 tube, a few inches above, has, in drying [cf. the figure to the left) become compressed 

 laterally in such manner as to appear conspicuously narrower at this point. The right-hand 

 figure of the same specimen, taken from a different point of view, shows, however, that 

 there is no actual narrowing of the lumen at the point named. 



Taking all the foregoing data into consideration, it would seem illogical, pending further 

 investigations, to adopt any other course than that of the provisional recognition of this 

 organism as a modified representative of the Zoantharia, distinguishable from all previously- 

 recorded types of that order by its habit of building up an erect tubular support, or, as 

 it might be appropriately designated, a " zoothecium." A new generic title — none of the 

 older ones befitting it — being required for its distinction, that of Acrozoanthus [Akros, high, 

 tall, Zoantlnis) is herewith provisionally proposed, the specific one of Australias, being 



