REPORT ON CORALS—HYDROCORALLINA. 39 
tissue composed of ccenosarcal meshwork zooids and gonophores, which may be called 
the living lamina. 
The canals of the ccenosare are composed of a very thin and transparent membranous 
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 ccenosare 
of Millepora as described and figured in the first part of this memoir. 
The ectoderm layer covering the ccenosarcal canals varies much in thickness, being 
thickest in the more superficial parts of the ccenosarcal 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 ccenosarc, 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 characterises it 
throughout. The layer investing the canals is mainly composed (Pl. XI. 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 presently described are contained in various 
stages of development. 
The calcareous matter of the ccenosteum must be secreted by this ectodermal layer of 
the coenosarcal canals, but 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 endodermal 
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 
eranular contents (Pl. XI. fig. 14). The arrangement of these several constituents of the 
endoderm within the lining of the canals was not determined. No doubt in all the 
Stylasteridee 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. 
As will be seen by reference to Plate HI., the ccenosarcal canals form in Spora- 
dopora a very complex network, which brings, by means of the freest anastomoses in all 
directions, the several members of the compound organism into complete circulatory 
connection with one another. 
The interspaces in the meshwork, occupied in the recent condition of the coral by hard 
masses of the coenosteum, are larger and wider in the deeper regions of the ccenosare than 
