226 THE NATURALIST IN AUSTRALIA. 



Roebuck Bay, in much more abundant colonies than had been before observed, and 

 also under conditions that yielded a satisfactory solution of the difficulties that had 

 previously prevented the determination of its precise zoological position and affinities. 

 The occurrence of a Zoantharian or polype community that built for itself a hollow' 

 tubular axis was hitherto unknown, and the interpretation that first presented itself 

 to the writer's mind with relation to the earliest observed examples obtained at Port 

 Darwin in the year 1888 (" Great Barrier Reef," p. 154) was that the organism was not 

 improbably a worm tube, parasitically encrusted by a typical Zoanthus. This first 

 impression, which was also shared, and has since been more emphatically advocated, 

 by another coelenterate specialist, Professor R. C. Haddon, has eventually proved to 

 be correct. At the same time, the fact that in none of the examples previously 

 obtained could any trace of a worm be found, added to the essentially unique character 

 and growth contour of the tubular structure, necessitated the provisional treatment 

 of the investing polyps and their nodulated hollow support as integral elements of the 

 same organism. 



From the abundant material obtained at Roebuck Bay, the full exposition of 

 the nature and habits of this interesting type is rendered practical, and more especially 

 with the aid of the photograph reproduced in Plate XL. Fig. 1 of this Plate depicts 

 the terminal half of a typical basal core denuded of its investing polyps, as washed 

 up on the coral beach. The regularity of the alternating growth-nodes and their 

 projection on the same plane are particularly distinct in this specimen. Fig. 2 portrays 

 an abnormal, bifurcating, tube. Fig. 3 in the same Plate represents a complete, 

 living colony-stock reproduced to a scale of one-third of its natural size, which, 

 having been photographed in its native element, shows many of the polyps in a 

 state of semi-expansion. This specimen, with others, had to be transported across 

 country and, being for many hours isolated from its native element, the polyps refused 

 under such circumstances to display their tentacular crowns to greater advantage. A 

 portion of the terminal half of this compound polypary is reproduced more nearly the 

 natural size in Fig. 4, in which the grouping of the polyps on the projecting angles 

 of the axial core is very distinctly shown. 



The most interesting figure in this Plate is, probably, the bottom one, Fig. 5, 

 which illustrates the precise conditions under which this organism grows and is left for 

 a while uncovered at low spring tides. As many as twenty-five separate polyparies or 

 colony-stocks of Acrozoanthus are here discernible on one side of an isolated rock, 

 which is, throughout the interspaces, coated with a matted growth of seaweeds, 



