ros) LE GREAT BARKIED REEF OF AUSTRALIA. 457 
positions in shallow parts, or when they had expanded in his tanks 
and tubs. 
Among the Alcyonarians, the Alcyonide, from their number and 
abundance, are very conspicuous on the living reefs; but as their 
most abundant forms possess a flexible corallum with separated 
spicules of lime, they break up on death and add only to the general 
powdery débris. 
Tubipora, the organ-pipe coral, is present for the most part not 
in large patches, but scattered about further inshore than ordinary 
corals, and in regions where there is much muddy sediment. Helzo- 
pova cevulea was found in abundance, and while the author now 
confirms Moseley’s reference of the Heliopores to the Alcyonarians, 
he is inclined to believe that a part of the corallum is built up by 
commensal worms closely allied to the Leucodore ciliata, which did so 
much to destroy the Australian oyster-fisheries. The account in the 
book, however, would be equally consistent with a purely parasitic 
relation of the worm to the coral. 
A new sheaf-shaped Alcyonarian, called Xenia pulsitans by the 
author, and found in Torres Strait, is remarkable not only for the 
size and delicate colouration of its polyps, but for certain special 
physiological manifestations. ‘‘ The expanded tentacles in this type 
measure over an inch in diameter. ‘The colour of the stalks and of 
the main shafts of the tentacles is a pale beryl-green, while the 
conspicuous tentacular pinnae, and the substance of the common 
supporting polypary, are a pale ochreous-brown. The special physio- 
logical phenomenon observed of this type was associated with the 
movements of its tentacles. In all ordinary polyps, whether belong- 
ing to the coral-secreting or skeletonless sections, the component 
tentacles move quite independently of one another, and their action is 
either irregularly vermiculate, or one of simple expansion and 
retraction. In the present type, on the contrary, all the eight 
tentacles move synchronously, opening out and contracting in a 
continuous measured rhythm, averaging two seconds to each con- 
traction. The action thus cbserved was in all respects identical 
with the pulsating contractions of a jelly-fish, and was suggestive of 
a less remote affinity between the Alcyonarian tribe and the medusi- 
form Hydrozoa than subsists between the last-named tribe and 
the coral-forming Madreporaria or skeletonless Actinozoa. This 
suggestion of affinity receives substantial support from the fact that 
as the radial processes throughout the jelly-fish tribe are invariably a 
multiple of four, and most commonly eight, they thus correspond in 
number with the tentacular organs of an Alcyonarian.” 
Among the Hydrozoa the only generic type that contributes tc 
any material extent to the formation of the reef is that of Millepora. 
The brilliant Dzstichopova coccinea, which resembles Corallium rubrum 
except that its skeleton is commercially valueless, is found not 
infrequently. 
