On the Structure and Relations of certain Corals. 149 



coral were carefully 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 ccenen- 

 chym, 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 ccenenchym, but 

 larger. They are said by M. -Edwards to have twelve septa appear- 

 ing as plications of the wall of their cavities. The number is, 

 however, very variable. I^he tabula? of the calicle are exactly 

 similar in structure to those of the ccenenchym. The hard tissue 

 is composed of doubly refracting calcareous matter, which has a 

 half-crystalline, half-fibrous structure. It is disposed 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 continue 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 calcareous 

 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 Corallium and Tuhipora* . 



The deep blue colouring of the corallum of Heliopora is due 

 to an amorphous colouring-matter insoluble in strong hydrochloric 

 acid, but soluble in acidified alcohol. It forms an intensely blue 

 solution of a sulphate of copper colour, which ti-ansmits the blue 

 and part of the green only of the spectrum. 



In the soft tissues of Heliopora an ectoderm, entoderm, and 

 mesoderm are to be distinguished. The ectoderm is composed of 

 club-shaped cells ; it has the usual disposition. Small oval nema- 

 tocysts are present in it and in the upper part of the mesodermic 

 laver beneath. The mesoderm consists of three histological elements, 



* The fact that the coraUura is so formed in Tuhipora seems to have been 

 hitherto unknown (Clans, ' Grundziige der Zoologie,' 3*" Aufl. p. 204). It is 

 plainly shown at the month of any growing tnbe in spirit specimens. Pro- 

 fessor Wyville Thomson drew my attention to the fact, an account of which 

 he thinks has been published by Professor Perceval Wright in the 'Annals 

 and Magazine of Natural History" 



