REPORT ON CORALS—HELIOPORID. 115 
the polyps of the Heliopora. Hence, possibly, the observed lack of propagation of applied 
stimulus. In their later work’ they write as follows :—‘ M. de Blainville’s observations 
on the animal of Heliopora caerulea led him to remove it from the genus Pocillopora, in 
which it had before been placed, and to form the genus Heliopora for it, because the 
animals of Pocillopora have never more or less than twelve tentacles. Heliopora has 
either fifteen or sixteen short, broad, triangular, pointed tentacles forming a disc around 
the mouth. The animals were made out with difficulty with a powerful lens.” Hight 
compound tentacles appear to have been mistaken by the observers for sixteen simple 
ones. 
Stomach.—The stomach of Heliopora is closely similar to that of other Alcyonarians. 
As seen in the contracted condition its walls are horizontally plicate. In transverse 
sections, as Plate I. fig. 3, the layers composing its walls are well seen. There is the 
usual covering of the endoderm ; but in the mesoderm, within the layer of homogeneous 
connective tissue, a second narrow zone (Pl. I. fig. 8, B) can be detected which is 
probably muscular. The inner ectodermal lining of the stomach is continuous with that 
of the tentacles, but ciliated. 
Mesenteries and Muscles.—Eight mesenteries completely divide the upper part of the 
cavity of the polyp into eight radially-disposed chambers. The mesenteries consist of a 
median plate of homogeneous connective tissue, which is directly continuous with the similar 
layer of the lining membrane of the calicular cavity, and also with that surrounding 
the stomach, and of an investment of endodermal cells covering the median plate on both 
sides, excepting where the retractor muscles intervene between the two. The retractor 
muscles form the lower borders of the mesenteries; they consist of long stout fibres 
which, lying on the surface of the mesenteries, take origin from the lower part of the 
sides of the polyp-cavity, and reach sometimes as far down as the margin of the tabula. 
They curve thence inwards and upwards, becoming gradually more concentrated as they 
ascend, and are inserted round the mouth and region just below it, in the intervals 
between the bases of the tentacles. 
The muscles have in position, with regard to the plates of the mesenteries, the same 
arrangement which Kélliker’ has described as existing in the Pennatulide,’ and which 
has also been found in the genus Umbellula by Lindahl and figured by him.’ 
The arrangement of the muscles is seen in Plate I. fig. 3, where R M, R M are 
the muscles. At opposite ends of the long axis of the stomach the muscles are on 
2 Quoy et Gaimard, Voyage de la Corvette l’Astrolabe, Paris, 1832, t. iv., Zoophytes, pp. 252, 253. 
2 Prof. Kélliker, Anatomisch-systematische Beschreibung der Alcyonarien, Abh. dersensk. naturf. Gesell, Frankfurt, 
1870. 
3 “Om Pennatulidslagtet Umbellula,” Kongl. Vet. Akad. inlemnad den 10, Feb. 1874 : Stockholm, tab i. fig. 5. 
4 Professor Schneider and M. Rotteken must certainly have been mistaken in their conclusions concerning 
the arrangement of the muscles with regard to the mesenteries in Aleyonaria, if the figure given in the Ann. 
and Mag. Nat. Hist., 1871, vol. vii. p. 437, as representing them be correct. 
