Millepora and Stromatopora. 303 
Millepora Woodwardit). Internal structure :—The surface, as 
already intimated, is the outward limit of a subjacent cancellated 
structure (fig. 5, b 6), formed by the anastomosis of more or less 
flattened reticulated fibre; and this, which is the staple sub- 
stance of the corallum, is remarkable for its minuteness and the 
tortuous form of both its solid and cavernous parts, the latter 
in the fresh state being occupied by the ccenosare, which is 
thus brought into direct continuation with the exterior. After 
forming a layer of about 1-180th inch in thickness and of 
yellowish-white colour, it becomes more compact and presents 
a bluish tint, which thus establishes a distinct line of demar- 
cation between the two; while, when the superficial layer is 
carefully picked off with a sharp point, the horizontal surface 
of the subjacent one is seen to be traversed by a deep grooved 
venation similar to that of Hydractinia arborescens, &c., with 
here and there the remains of a dry sarcodic ccenosarcal tube 
in it running along its course, thus indicating that the surface- 
layer, which is less compact, of a different colour, and overrun 
here and there by a tubular venation, is the external layer of 
the growing corallum; and therefore we may fairly infer that 
successively the corallum has been formed in this way through- 
out, although somewhat modified in density &c. by age and 
subsequent development. 
Having now described the staple substance of the corallum 
from the surface to the axis of the branch (that is, from the 
circumference to the centre), we have next to follow the large 
apertures in the same way. These, in the vertical section, 
may be observed to be the openings of tubular spaces varying 
from 1-360th to 1-180th inch in diameter, which descend more 
or less vertically and nearly to the central plane that separates 
the two lamine of which the elkhorn-like compressed branch 
is formed (fig. 5,aa). Further, it may be observed that 
these spaces are horizontally but unequally divided into 
several compartments by very thin transverse septa or tabule 
(fig. 5, c), and that their internal surface is plentifully perfo- 
rated by more or less rounded apertures (fig. 5, e) such as may 
be seen in Stromatopora, which communicate with the tortu- 
ous cavities of the coenosarcal skeleton or cancellated structure 
of the corallum, so that the tubular spaces are as much fora- 
minated (fig. 5, c,d) as the coenosarcal skeleton is cancellated, 
being simply excavated in the midst of the latter, without the 
least trace of any distinct parietes after the coenosarc has 
been abstracted. Indeed it is very remarkable that all 
the cavities of the ccenosarcal skeleton (that is, of the 
whole corallum, like that of Parkeria &c.) are formed 
upon the ccenosare (identical in this respect with the can- 
