106 
ME. H. N. MOSELEY ON THE 
Openings to the exterior other than those of the polyps were carefully sought for 
over the surface of Heliopora , but without success. The spots from which, by decalci- 
fication, growing tips of corallum have been removed, often form themselves into 
apertures in horizontal sections, and are apt to mislead the observer. 
Structure of the Polyps of Heliopora. 
The polyps of Heliopora have been examined by me only in a contracted condition. 
When the contracted polyps are viewed from the interior they show (Plate 8. fig. 5) 
eight symmetrically and radially disposed lobes, separated by deep sulci corresponding 
to the insertions of the eight mesenteries into what would be, in the expanded condition 
of the animal, part of the lateral wall of the polyp. The lobes show a distinct striation 
in the direction of their length, indicating probably the presence of fine muscular 
fibres in their substance. At their inner region the lobes show, near their common 
centre, a number of extremely small nuclei upon their surface. The lobes just 
described form a covering closing the mouth of the calicle. 
From the centre of the disk of lobes a tubular cavity, which may be called the 
atrium, leads down directly to the mouth (Plate 8. fig. 1) ; and around the mouth and 
just above it orifices of the eight tubular introverted tentacles open into the atrium. 
The tentacles in the retracted condition are completely introverted and appear as 
tubes, the inner cavities of which would, in the expanded condition of the polyp, form 
the outer surface of the tentacle. The cavities of the introverted tentacles communicate 
directly with the atrium, as may be seen in vertical sections, by orifices which show in 
the centre a cruciform lumen (Plate 8. fig. 1, T') formed by the folds of the ectodermic 
lining of the tentacular cavity. The retracted tentacles are directed at first horizontally 
outward from the atrium, and then turned downwards at nearly right angles to their 
former course. The tentacles rest in the intermesenterial spaces. Transverse sections 
of four of them are seen in Plate 8. fig. 3. The cavities of the introverted tentacles 
are lined by a direct continuation of the ectoderm, which passes down over the inner 
surface of the atrium to enter these cavities. In their interior it is elevated into a 
series of short stout tubercles, which no doubt project much more in the expanded 
condition of the tentacle, rendering it compound as in other Alcyonarians. In the 
tentacles, as seen in Plate 8. fig. 3, three layers, outer entodermic, median connective- 
tissue, and inner ectodermic, can be readily distinguished. The median probably 
contains muscular structures, but I have been unable to see them. 
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 8. fig. 3, the layers composing its walls are well seen. There is the usual 
covering of the entoderm ; but in the mesoderm, within the layer of homogeneous con- 
nective-tissue, a second narrow zone (B, fig. 8) can be detected, which is probably 
muscular. The inner ectodermic lining is continuous with that of the tentacles, but 
ciliate. Eight mesenteries completely divide the upper part of the cavity of the polyp 
