REPORT ON CORALS—HYDROCORALLINA. 13 
SECTION I—ON THE STRUCTURE OF THE MILLEPORIDA. 
INTRODUCTION. 
In a paper treating mainly of the structure of Heliopora cerulea which was com- 
municated to the Royal Society in the autumn of 1875,' I gave a short account of the result 
at which I had arrived from the examination of two species of Millepora, obtained at 
Bermuda and at the Philippines, and expressed my intention of further prosecuting the 
subject at the Sandwich Islands and Tahiti, should material be forthcoming. 
At Honolulu no Millepora was met with; and this form apparently does not occur 
at the Sandwich Islands, the water being too cold for it. At Tahiti a Millepora is very 
abundant on the reefs, in from 1 to 2 feet of water, and is very conspicuous because of 
its bright yellow colour. 
I failed in an attempt to procure the animals of this species in an expanded condi- 
tion; but my colleague, Mr J. Murray, succeeded on two occasions, and on the second 
occasion showed me the expanded zooids, and handed the living specimens over to me 
for examination. I am greatly indebted to Mr Murray for having thus afforded me the 
opportunity of studying the zooids of Millepora in the expanded condition, and I do 
not think that I should ever have succeeded in arriving at a satisfactory knowledge of 
their structure without this aid. Mr Murray further, who had had better opportunities 
of observing the living coral than I, first drew my attention to the fact that the central 
zooid of each system had a mouth. No species of Millepora appears hitherto to have 
been known to occur on the reefs of the Society Islands. In Dana’s work on Corals? 
no Millepora is mentioned as occurring at Tahiti, and this locality is not given for any 
species of Millepora by MM. Milne-Edwards and Haime. The Tahitian species, of which 
the structure is here described, was determined for me by my friend, the late Dr F. Briig- 
gemann, who, at the time of his death, was engaged in arranging and determining the 
collection of corals in the British Museum, to be Millepora nodosa of Esper.’ The 
species is mentioned by M. Milne-Edwards under Millepora gonagra;* it resembles closelyin 
form Millepora tuberculosa (Millepora gonagra), figured by MM. Milne-Edwards and Haime.’ 
Like this species, it never forms foliaceous expansions, but is tuberculate and irregular 
in shape, and often encrusting, commonly overgrowing the dead fronds of Lophoseris 
cactus, which is a principal component of the Tahitian reefs. The present species 
seems, however, to differ from Millepora tuberculosa in that its pores are disposed over 
1 Phil. Trans. Roy. Soc., vol. clxvi., 1876, part 1, p. 91. 
> United States’ Expl. Exped., vol. vii., Zoophytes, by J. D. Dana, Philad., 1846. 
3 Esper, Pflanzenthiere, vol. i. p. 199, Millep., pl. i. (1791). 
4 Hist. Nat. des Cor., vol. iii. p. 230. > Ihid., pl. xiii. tigs. la, 1b. 
