On the Structure and Relatiuns uf certain Corals. 157 



peculiarities in the structure of the soft parts, aucl the relations of 

 the tentacles to the septa, described in this paper as occurring 

 in a Stylaster and a Cnjptohelia, and the similar facts observed 

 by Sars in the genus Allojwra, strengthen the facts brought for- 

 ward by Pourtales, with regard to the coralla, in a very poten- 

 manner. I hope to make a close study of the structure of >Sti/- 

 laster. The apparent absence of mesenteries is most remarkable, 

 and a similar condition appears to occur also in Millcpora. The 

 number of tentacles and septa in the Stylasteridae seems hardly 

 to follow the usual hexameral law. In the species of Sttjlaster 

 examined by me there are invariably twenty-two septa and 

 twenty-two tentacles. In Stylaster enihescens, Pourtales describes 

 the septa as being in number from nine to twelve, most frequently 

 eleven. In Allopora miniata the septa are from seven to ten, gene- 

 rally eight. Cryptolielia has commonly sixteen. 



AVith regard to the affinities of the Milleporidfe, no certain con- 

 clusion can be arrived at from the few facts yet ascertained. I 

 hope to obtain specimens at Hawaii in sexually mature condition. 



H.M.S. ' Challenger,' ISTorth Pacific. 

 21st July, 1875. 



POSTSCEIPT. 



Since the above was written I have been able to refer at Hono- 

 lulu to Prof. Lacaze-Duthiers's ' Histoire Naturelle du Corail.' I 

 therefore add a few notes. 



In Corallium the contracted pol^'p presents externally at the 

 surface eight lobes coloured red. AVhen the polyp is expanded, 

 these lobes form a coloured cup with eight dentations at its mar- 

 gin, which surrounds the lower part of the expanded colourless 

 polyp (see pi. 2 of Prof. Lacaze-Duthiers's work). The eight lobes 

 described as closing the mouth of the calicle in the contracted 

 pol\"p of Heliopora probably oc<^-upy a similar position, and have a 

 similar appearance in the expanded condition of the polyp. 



In Corallium the pinnae or barbules of the tentacles are all 

 severally introverted (l^. p. 57), as well as the tentacles themselves. 

 In Ilellopora this appears not to be the case. In the hard tissue 

 of Corallmm boring vegetable parasites occur, as observed in Mil- 

 lepora and Pocillopora. 



I have further been able to refer to Dana's great work on 

 Corals in the splendid collection of scientific works in the Govern- 

 ment Library at Honolulu, and to other works relating to Helio- 

 pora. 



Dana states (U.S. Expl. Exped. vol. vii. Zoophytes, J. D. Dana, 

 Philad. 1846, p. 539) that the blue colour of Ileliojwra is of ani- 

 mal origin and is lost on immersion of the coral in nitric acid. 

 The colouring-matter was not analyzed by ^Ir. Gilliman. 



In the Atlas of the 'Voyage de I'Astrolabe,' Zoophytes, pi. 20. 

 figs. 12, 13, 14, the expanded polyps of Heliopora cfprulea are 

 figured bv MM. Ilombron and .lacqninot. In fig. 14 sixteen very 

 short, simple, conical tentacles are shown, in fig. 13 only fifteen 



