40 THE VOYAGE OF H.M.S. CHALLENGER. 
nearer to the external surface; for here the meshwork is much closer, and the mass of 
soft living tissue much greater in proportion to the calcareous structures secreted by it, 
than is the case in the deeper regions. Further, the deeper canals are of greater calibre 
than those nearer the surface. Towards the deepest regions of the coenosare the canals 
are shrunken and atrophied, and pass off into effete and almost dead fragments of tissue, 
which form the inner boundary of the living lamina. 
The largest trunks of the meshwork are those which proceed directly from the bases 
of the zooids and gonophores. These are soon reduced in size by branching, and are lost 
in the general anastomosis. 
Around the sacs contaming the zooids the canals of the ccenosarc have a special 
radiate disposition (Pl. X. fig. 3). The radial canals occupy an area circular in outline 
extending all around the outer sides of the sacs of the zooids. They pass directly inwards 
radially, from the margins of the areas where they take origin from the general meshwork 
to join themselves on to the walls of the zooid sacs, towards the centres of the areas. 
They branch but seldom on their course, and then only towards their outer origins 
where they not uncommonly bifurcate. 
As may be seen from the figure, the radial canals, which he at successive depths 
from the surface, do not correspond in any way in position with those above or below 
them, but are quite irregular as far as radial disposition is concerned. In vertical 
sections, however, of the living lamina (PI. III.), these radial canals are seen to succeed 
one another at tolerably regular intervals, in vertical disposition, with a somewhat regular 
series of interspaces between them. 
This radial disposition of the canals is less marked around the saes of the larger 
dactylozooids than around those of the gastrozooids, and is hardly apparent around those 
of the smaller dactylozooids. Traces of it are to be seen around the sacs of the gono- 
phores, as at G’, Plate XXXVI. Although towards the periphery of the area occupied 
by them these radial canals contain endoderm cells, and appear similar in structure to 
the other canals of the ccenosare, towards their inner extremities, where they join the 
zooid sacs, they become diminished in size, and often appear as mere slips of transparent 
tissue having a fibrillate appearance. 
Muscular filaments, continued from ovoid muscular cells embedded in the walls of 
the zooid sacs, pass outwards along the radial offsets, and are attached to them in the 
region about the mouths of the sacs (Pl. X. fig. 3, RM). 
Attached to the radial offsets, and often extending over the interspaces between 
adjacent ones, slips of a fine transparent membrane, containing minute nuclei and 
striated in appearance as if composed of fine fibrillxe, are constantly to be seen; but 
they seem to occur at altogether irregular intervals, and only towards the more super- 
ficially lying parts of the zooid saes (PI. X. fig. 3; Pl. IH. AA). 
A continuous layer of ectodermal tissue extends over the outer surface of the coral. 
