152 THE GREAT BARRIER REEF. 



budding, unattended by separation from the parent pol^'p, form associated colony-stocks, 

 have been relegated by biologists to the order of the Zoantharia. 



The broad external feature that readily serves to distinguish the members of the social 

 anemone order now under consideration, from their Alcyonarian allies, is the number of tentacles 

 they respectively possess. These organs in the last-named group are invariably eight, while 

 among the Zoantharia, as in the simple Actinaria, they are either a multiple of six or indefinitely 

 innumerable. Again, whilst the tentacles of the Alcyonarian polyps are most commonly fringed 

 or pinnate, those of all known Zoantharia are, without exception, perfectly simple. Among the 

 types of the Zoantharian order that form a fitting parallel to certain Alcyonarian species, refer- 

 ence may be made to the very beautiful little variety, apparently identical with Zoaiiflms 

 Coppiiigcri, illustrated by Fig. ii of Plate III. of the chromo-lithographic series, which may 

 be fitly described as one of the gems of this group. The combination and arrangement of the 

 colours in this species are almost an exact counterpart of what obtains in the Alcyonarian 

 form Cornnlaria aiirkula, represented by Fig. 8 of the same plate. Both specimens possess, in 

 common, green oral centres surrounded by a fringe of rich brown tentacles. In the one instance, 

 however, the tentacles are only eight, while in the other they are practically indefinite. The 

 green oral centres in the Zoanthus figured were of exceptional brilliance ; in other examples 

 observed, this area was sometimes a lighter and duller green, and in other instances a darker 

 bottle-green tint. The supporting base in this type, as also in the majority of the Zoantharia, 

 is represented by a continuous fleshy expansion known as the " cosnosarc," in place of a 

 subcylindrical creeping stolon such as obtains in Cornularia. 



A second type of the Zoantharian series, Palythoa casia, is illustrated by Fig. i of Chromo 

 plate No. III. The polyps in this form are not elevated on separate contractile stalks as in the 

 foregoing species, but open out directly on mammiform elevations of the surface of the connecting 

 " coenosarc." The tentacles, moreover, are exceedingly short and rudimentary, forming a single 

 incurved circlet round the inner margin of the hollow, crater-like, polyp-papillae. As indicated 

 in the accompan3'ing illustration, the ordinary colour of the combined coenosarc and polyp- 

 elevations of this Zoantharian is a rich creamy-yellow, varying, however, to a lighter or darker 

 shade in different colony-stocks, the circlet of minute tentacles in all instances being a more 

 distinct brown. Patches of this composite polyp not unfrequently spread, as an incrustation, 

 over reef-areas several yards in extent, and, in many instances, over the dead coralla of 

 Meandrinae, Goniastraeas, or other Astraeacsese. Under these last-named conditions, the Palythoa 

 is somewhat liable to be mistaken for a solid Madreporarian. 



A third and altogether unique modification of the Zoantharian structural tj'pe is exemplified 

 by Chromo plate No. III., Figs. 4 and 4A. In this form, the associated polyps, in place of forming 

 flattened adherent masses, build up an erect polypary that at first sight might be mistaken for a 

 solid corallum. This polypary consists, however, of a tubular irregularly nodular central axis, 



