146 THE GREAT BARRIER REEF. 



would be parallel with that which has been supposed to subsist between the pilot fish and the 

 shark ; the commensals, in return for shelter and protection from fiercer foes, fulfilling for their 

 hosts the role of effective lures. 



Among the sea-anemones of the Barrier district noteworthy for their beauty of structure 

 rather than that of colour, two representatives of the respective genera Actinodendron and 

 Megalactis invite special notice. In the members of the first-named genus the tentacles, 

 or their arm-like homologues, are twenty-four in number, exceedingly long in comparison with 

 the diameter of the disk, and ramified, after the manner of the fronds of many ferns or sea- 

 weeds, to a degree which is technically termed tripinnate or even bi-tripinnate. Their aspect 

 v\'hen fully expanded in the sandy hollows among the coral-rocks, or in pools nearer in- 

 shore, so much resembles that of symmetrical tufts of growing seaweed that they may be 

 easily mistaken for such vegetable organisms. They are, doubtless, innocently approached 

 under such an impression, and to their own undoing, by the living animals on which they 

 feed, which realise the fatal error they have committed too late to make good their retreat. 

 The species under consideration, Actinodendron alcyonoideum, moreover, is noted for stinging 

 properties which are nearly as severe as those of a nettle, while the rash raised by handling 

 it, as experimentally tested b3' the author, lasts for about a week. In this type the stem 

 or column, with its adhesive base, is usually rooted, to a depth of a foot or more beneath 

 the sand, to a substratum of the solid coral-rock. The polyp is furthermore very difficult to 

 detach intact, on account of the great fragility of the branching tentacles, which are apt to 

 adhere to the hand and break up, piecemeal, in the attempt to root it up. Under these con- 

 ditions it was found that the only efilectual method of securing an unbroken crown of tentacles 

 was to insert a long, sharp knife underneath the sand, and to then sever the column as near 

 as possible to its adherent base. The illustration of this species given in Plate XXII., No. i, 

 of the photo-mezzotype series, is reproduced from a photograph taken of the anemone when 

 expanded in situ, in a pool on the sandy flat adjacent to the fringing coral-reefs off Somerset, 

 in the Albany Pass. Larger specimens not unfrequently occur which are twice the diameter 

 of the example figured. Its colours in life are usually of a light stone-grey, the extreme tips 

 of the minute tentacular ramifications being almost white. 



The second species of branching-armed anemone represented by the lower of the two 

 figures in the plate above quoted has more attenuate tentacles than those of the preceding 

 type, while the ultimate ramifications are individually isolated and distinct. The oral disk 

 in the fully expanded polyp shows much more clearly, and, together with the tentacles, exhibits 

 a relatively elaborate colour pattern. As shown in the photograph from life also taken of this 

 type, twelve white radiating lines, corresponding with the axes of the six primary and six 

 secondary tentacular radii, and of distinct relative length, occupy the centre of the disk. 

 Outside these, again, there are twenty-lour shorter lines of even length (such as might make 



