68 COELENTERATA—CNIDARIA SUB-BRANCH II 
conducting into the gastric cavity. The outer covering of the body, whose 
parts are designated as wall, oral disk, and pedal disk, are constituted of 
ectoderm and entoderm, between which is a thin layer of mesoderm (Jesogloea). 
Six, eight, or more radially disposed vertical partitions (mesenteries), (Figs. 98, 99), 
projecting inwardly from the body-wall, divide the gastric cavity into a series 
of radiating compartments (mesenteric pouches). The mesenteries are prolonged 
upwardly as the hollow, muscular tentacles; while the generative organs are 
attached to their faces near the lower end of the body. The mesenteries are 
covered on both sides with muscular tissues, and bear mesenteric filaments on 
their curled inner edges. On one side of the mesenteries the muscle fibres are 
transversely directed, on the other longitudinally. The longitudinal system 
is usually considerably folded and thickened; and the disposition of these 
muscular portions (Juskelfahne) is of great importance from a systematic stand- 
point, since it reveals 
the bilateral symmetry 
of many Anthozoans, 
and enables one readily 
to identify the anti- 
meres. If a polyp in- 
dividual be cut in two 
by a plane passing 
through the longer axis 
of the mouth-opening, 
then, in the Octocoralla 
(Fig. 98), the mesen- 

Fic. 98. Fie 99. C : 
Diagrammatic section of Diagramiatic section of the soft parts of teries of the right half. 
the soft parts of an Octo- a Hexacoralla. In the upper half (above the will have all the mus- 
coralla (Aleyonium). «, Oeso- line a—b) the section passes through oeso- i : f 
phagus; 1, 2, 3, 4, Mesen- phagus s; in lower half, beneath the same. cular thickenings dis- 
teries of the left side (after Corallum indicated by heavy lines. 7, direc- : 
R. Hertwig). tive mesenteries. posed on the right-hand 
side, and those of the 
left on the left-hand side. In the Hevacoralla (Fig. 99) the mesenteries are 
grouped in pairs, with the muscular thickenings of any pair facing each other. 
Two pairs, however (those corresponding with the opposite extremities of the 
longitudinal mouth), form often an exception to this rule, since these have the 
muscular thickenings placed on opposite sides. These are called the directive 
mesenteries, and serve to indicate the longitudinal axis of the body. 
Only a few Anthozow have permanently soft bodies ; the majority secreting 
caleareous, horny, or partly horny and partly calcareous structures, termed the 
skeleton or corallum. The simplest form of corallum is that composed of 
microscopic, round, cylindrical, acerate, or tuberculated spicules of carbonate of 
lime, which are developed in great quantities in the mesoderm and remain 
detached in the soft parts (many Aleyonaria). In a number of forms (Coralliwn, 
Mopsea, Tubipora) the spicules are firmly cemented together by means of a 
calcareous or horny connective substance, in such a manner as to form tubes 
(Lubipora), or, when the secretion takes place chiefly at the base, a sclerobase, 
or axis. Surrounding the axis is the soft coenosare in which the polyps of the 
colony are embedded (Fig. 100). In some cases the sclerobase is composed 
entirely of horny matter without admixture of calcareous secretions. In the 
so-called “stone corals” (Fig. 101) a consistent calcareous skeleton is formed 
by the outer surface of the ectoderm. At the base of the polyp between each 
