IV. On the structure and relations of the alcyonarian heliopora cærulea, with some account of anatomy of a species of sarcophyton, notes on the structure of species of the genera millepora, pocillopora, and stylaster, and remarks on the affinities of certain palœozoic corals
Having undertaken the examination of the Deep-sea Corals dredged by the ‘Challenger’ during her voyage, my attention was naturally directed to the study of the structure of corals generally. The Milleporidse, both because of their peculiar tabulate structure and relations to fossil forms, and because of Prof. A gassiz’s well-known determination of them as Hydroids and not Actinozoa, seemed to offer the most interesting field for investigation ; and I accordingly commenced the examination of their structure very early in the cruise of H. M. S. ‘Challenger’ in April 1873, at Bermuda, where Millepora alcicornis occurs in great profusion. I made a number of preparations and made out some points in the anatomy of this species, but found the subject to be so difficult that I put the matter aside to be further examined on reaching England. In the beginning of 1875, however, I obtained specimens of Heliopora caerulea in the living state at Zamboangan, and on examining these found to my astonishment that Heliopora was an Alcyonarian. I therefore during subsequent voyages made as complete an examination as possible of this species, and examined for comparison with it the structure of another Alcyonarian, a species of Sarcophyton dredged in shallow water amongst the reefs of the Admiralty Islands. I examined further the structure of a species of Millepora obtained at Zamboangan ; and I also examined a Pocillopora found at the same locality, and a species of Stylaster dredged in 500 fathoms off the Meangis Islands. The results form the substance of the present paper.