THE ANATOMY OF THE MADREPORARIA. 411 
longer than the rest. Coste, i.e. ridges on the outer face of 
the theca, correlated with the septa within, correspond to the 
primary septa, but die out at some distance from the base. 
The relations of the body wall are in one respect peculiar. 
The Galaxea colony consists of (1) the polyps with their thece ; 
they are free, i.e. do not touch one another laterally, but spring 
independently from (2) a plate-like cenenchyme which encrusts 
dead coral or rock. The body wall is continued (outwards and 
downwards from the oral disc) over the lip of the theca, and 
is supported in the usual manner for a certain distance on 
the peripheral lamelle of the mesenteries. The latter then 
cease, and the body wall extends as a loose sheet down the 
side of the theca, over the plate of coenenchyme, and up the 
sides of the polyps next adjacent. A vertical section between 
two polyps shows therefore (1) the body wall of ectoderm, 
mesogloea, and endoderm ; (2) a space, part of the common 
celenteron of the colony; (3) a layer of endoderm, meso- 
gloea and (?) calicoblasts which directly overlies (4) the 
coenenchyme itself. 
Sections of a larger polyp showed six primary, six secondary, 
and twelve tertiary entocclic septa; twenty-four pairs of 
mesenteries ; twenty-four entoccelic, and, apparently, twenty- 
four ectoceelic tentacles. It is not, however, possible to speak 
with certainty as to the presence of ectoccelic tentacles in this 
and many other Madreporaria in which the ectoderm is not 
specially differentiated into batteries, without an inspection of 
the living expanded animal; since folds of the oral disc may 
easily be misinterpreted in this connection. 
The mesenteries do not extend quite to the bottom of the 
polyp cavity; at the point where they cease a change occurs in 
the character of the endoderm; elsewhere composed of the 
ordinary cubical cells, it swells here into such long vacuolated 
cells as to completely obliterate the interseptal spaces. Well- 
developed calicoblasts of the type already figured for Lophohelia 
« Anat. Madr.,”’ iii, fig. 8) occur at the growing points of the 
coral. In other respects the histological characters do not 
call for comment. No generative organs occurred in my speci- 
