1875.] Structure and Relations of certain Corals. 61 



to be Hydroids. Favosites, with many other genera of Palaeozoic Corals, 

 he considers to be a Bryozoon. 



Methods employed. — The corals examined were hardened in alcohol or 

 chromic acid, decalcified, and cut into fine vertical and horizontal sections. 

 Sections of the hard parts were rubbed down in the usual manner. 

 Portions of Heliopora ccerulea were also examined in the fresh state. 



On the Structure of Heliopora caerulea. — Heliopora ccerulea was found 

 growing in abundance on reefs near Zamboangan at low tide. The 

 polyps were never seen expanded, though pieces of the coral were care- 

 fully transferred to a glass vessel without being removed from the water. 

 The living coral is perforated in all directions by a parasitic Annelid 

 (Leucodora). The corallum of Heliopora is remarkable for the tubular 

 character of its coenenchym, which consists of a series of tubes arranged 

 side by side at right angles to the surface of the coral, open above but 

 closed below by successive transverse partitions or " tabulae." The calicles 

 are tubes essentially similar to the tubes of the coenenchym, but larger. 

 They are said by M. -Edwards to have twelve septa appearing as plications 

 of the wall of their cavities. The number is, however, very variable. 

 The tabulae of the calicle are exactly similar in structure to those of the 

 coenenchym. The hard tissue is composed of doubly refracting calcareous 

 matter, which has a half-crystalline, half-fibrous structure. It is dis- 

 posed in a series of systems vertically to the surface of the corallum, the 

 axes of which systems lie in the interspaces between the coenenchymal 

 tubes. In each system the fibres of hard tissue are disposed radially 

 around the central vertical axes, and at the same time with an upward 

 inclination at an equal angle all around. 



The colony of Heliopora is developed entirely by budding. In a 

 growing point of the corallum the coenenchymal tubes are widely open 

 and polygonal in outline. New calicles are formed by the junction of a 

 number of tubes around a central tube or tubes arrested in growth 

 which form a base. The outer walls only of the surrounding tubes con- 

 tinue to grow and form the lateral wall of the calicle. The newly 

 formed calicle thus has tubular prolongations at its base, and the so- 

 called septa are, in the main, due to the circumstance that the wall is 

 composed of a series of fused curved outer walls of tubes. The calca- 

 reous matter is deposited in a finely fibrous calciferous tissue, connected 

 apparently with the formation of which is a layer of connective tissue 

 which everywhere covers the hard parts. 



There is no trace of the corallum of Heliopora being composed of fused 

 spicules as in the case of Cor allium and Tubipora*. 



* The fact that the corallum is so formed in Tithipora seems to have been hitherto 

 unknown (Claus, ' Grundziige der Zoologie,' 3 e Aufl. p. 204). It is plainly shown at the 

 mouth of any growing tube in spirit specimens. Professor Wyville Thomson drew 

 my attention to the fact, an account of which he thinks has been published by Pro- 

 fessor Perceval "Wright in the ' Annals and Magazine of Natural History.' 



