1894.] Affinities of Heliopora cserulea, $c. 301 



be specialised parts of a system of inosculating endodermic canals, 

 such as are characteristic of colonial Alcyonaria. 



The corallum of Heliopora exhibits two sets of apertures, besides 

 those due to the inroads of boring parasites, these are the calicles and 

 the coenenchymal fenestrce. The calicle cavities are occupied by the 

 polyps, the coenenchymal tubes, whose mouths are the fenestrae, are 

 occupied by the cceca, which do not in the fresh condition open to the 

 surface, the fenestroe being closed above by the ectoderm. 



The corallum consists of an imaginary vertical plane, occupied by 

 vertically disposed ccenenehymal tubes, and right and left faces on 

 which the tubes open after bending sharply from the vertical to take 

 a short horizontal course. The vertical tubes are in section polygonal, 

 and some of them attain, the surface at the growing edge. Those 

 which are deflected hoi'izon bally become thickened by the formation 

 of secondary calcareous deposits inside the primitively polygonal 

 tubes. The calicles are formed by the arrest in growth of groups of 

 ccenenchymal tubes as they approach the surface. The cavity of a 

 calicle never extends into the central vertical tubes. 



The walls of each ccenenchymal tube are primarily formed of 

 twelve delicate calcareous laminae, secreted by the calicoblasts 

 covering the ccenenchymal cceca, and have this peculiarity, that each 

 of the laminae takes a sbai'e in the formation of the walls of 

 adjacent tubes. As seen in section, three lamina? are united at each 

 angle of the generally hexagonal tube to form a Y' s ^ a P e( l figure. 

 Each arm of the Y m eets, and is united by sutures with the arms of 

 adjacent Y' s > an( ^ so a sor * ; f honeycomb structure is produced, 

 which, if the symmetry of growth were perfectly regular, would 

 consist of a series of regular hexagons. The symmetry is disturbed 

 by the multiplication of the tubes, which do not branch dichoto- 

 mously, as in the allied Heliolites, but increase by the addition and 

 intercalation of new tubes amongst those previously existing. The 

 hexagonal primary constituents of the corallum of Heliopora show 

 very slight traces of blue colour, but as they become thickened by 

 secondary ring-shaped deposits, the latter develop blue pigment, and 

 give the characteristic colour to the colony. 



The growth of the colony is not effected, as Moseley described, by 

 the upgrowth of an axial polyp from which lateral buds are given off, 

 but by the rapid growth and multiplication of coenenchymal tubes. 



The fact that the calicles and coenenchymal tubes of Heliopora have 

 not each their distinct and proper wall, but that their walls are 

 common to them and to adjacent tubes, is a characteristic feature of 

 Heliopora and its allies. I therefore propose for them the name 

 Ccenothecalia, in contradistinction to those forms in which, as in 

 Tubipora, each corallite is separate and distinct ; the latter group 

 may be called the Autothecalia. 



