432 MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTERID2E. 
condition of the coral by a series of mesh works of correspondingly branching, 
twisting, and anastomosing canals, which compose the coenosarc or common body of 
the compound organism in each case. In Sporadopora, only a comparatively thin 
layer on the surface of the coral is occupied by living soft structures. These living 
structures are separated from the non-living deeper masses of the corallum by the 
action of acids, and then appear as a sheet of soft tissue composed of coenosarcal mesh- 
work zooids and gonophores, which may be called the living lamina. 
The canals of the coenosarc are composed of a very thin and transparent mem- 
branous wall, covered on the outer surface by a layer of ectoderm cells, and on the 
inner lined by endoderm cells. In general structure the canals closely resemble those 
of the coenosarc of Millepora as described and figured by me. (“ On the Structure of 
Species of Millepora occurring at Tahiti, Society Islands,” Phil. Trans. Roy. Soc., 
1877, p. 9, Plate 3, fig. 16). 
The ectoderm layer covering the coenosarcal canals varies much in thickness, being 
thickest in the more superficial parts of the coenosarcal meshwork. I was, 
unfortunately, unable to examine its structure in the fresh condition, because the 
trawl by which the specimens of Sporadopora and of most of the other genera were 
obtained came up late in the day, and the short daylight available sufficed only for 
the investigation of more important matters. 
Although a definite cell structure is not to be made out everywhere in the 
ectoderm of the coenosarc, as for example in the surface layer of the coral, it seems 
probable from the appearances presented by specimens hardened in osmic acid, that 
such characterizes it throughout. The layer investing the canals is mainly composed 
(Plate 44, fig. 13) of transparent inflated nucleated cells which vary in size, so that 
the stratum is in some places two cells thick, in others only one. Amongst these 
cells occur nuclei and certain cells in which nematocysts of two kinds to be pre- 
sently described are contained in various stages of development. 
The calcareous matter of the corallum must he secreted by this ectodermal layer of 
the coenosarcal canals, hut I have not been able to observe how this takes place, or 
whether by means of any particular form of cell. 
In the membranous layer of the canals no structure was detected. The endo- 
dermal lining of the canals is composed of abundance of spheroidal pigmented cells, 
containing a nucleus and granules of pigment of various sizes, and closely similar in 
appearance to those occurring in Millepora. The pigment in the present species is of 
a brick-red colour. Besides these cells, smaller transparent, colourless, spheroidal 
cells occur in the endodermal layer, and also free pigment granules and effete pigment 
cells, devoid of granular contents (Plate 44, fig. 1 4). The arrangement of these 
several constituents of the endoderm within the lining of the canals was not deter- 
mined. No doubt in all the Stylasteridse the inner surface of the canals is, as usual, 
ciliated, although cilia were not able to be made out in any case, owing to the action 
of reagents on the tissues. 
