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free from the axial epithelium, except with some species ( Eucirr. contorta , Sibop. gephuro , 
ApJian. Sibogae ), where this septum is fused, in its lower part, with the axial entoderm and 
mesogloea, so that the polyps are completely separated one from the other. In the same Eucirri- 
batkes- species the interzooidal septum forms a more or less complete basal septum between the 
gastral cavity and the axis. This basal septum is complete in Stick, saccula , while Stick, semi- 
glabra has an incomplete basal septum, which is only complete at the polypar periphery. The 
basal septum may be fused with the free border of the primary transversal mesenteries. 
Axis-epithelia and axis. The axial ectoderm as well as the entoderm usually are thin 
layers only; the axial entoderm has the same structure as in the bodywall, except for the usual 
absence of glandular elements. In Sibop. gephura this entoderm contains large, deeply staining 
glandcells and in Euant. myriophylla many hyaline glandcells. I he mesogloea is homogeneous. 
The axial ectoderm is in structure very like the entoderm, e. g. as to the shape of the nuclei. 
Rarely there are some deeply staining elements in this ectoderm. 
The axial sheath is connected with the bodywall by a connecting septum ot mesogloea 
with entoderm, usually diametrically opposite the mouth. The septum is asymmetrically placed 
with some species, either always, or partly in a colony ( Bathyp . patula , Stickop. vanabilis). The 
septum is everywhere subequal in breadth, or triangular so that the base is found on the axial 
side, or double-funnelshaped, with its broad sides at the axis and at the bodywall. Over some 
distance the septum may be double. In the neighbourhood of the colony-top the septum broadens 
and is shorter, so that it is more like a fusion between the axial sheath and the bodywall 
over the greater part of the circumference. — In normal conditions the septum may also be 
more like a fusion as is found at the top of the spines. — There are a few microscopical 
indications, or none at all, of the longitudinal groove, which often may be found along the back 
of the axis at the macroscopical examination; Sckizop. apfinis and Bathyp. patula show a groove 
with thinner ectoderm and mesogloea, in the bodywall opposite the connecting septum, while 
also, but problematically, an invagination-opening is found between the doubled connecting- 
septum in Sckizop. afpnis. — The spines are entirely covered with the axial sheath; the axial 
ectoderm is the thickest at the base of the spines; the layers are very thin at the apex of the 
spines. When the spines are long or the gastral cavity very narrow, the spines repeatedly come 
so near the bodywall that the mesog'loea and the entoderm of the axis and of the bodywall are 
fused together. The same fact is possible for the spinal sheath and the mesenteries, and also the 
interzooidal septum. — Sometimes the free border of the primary transversal mesenteries is 
entirely fused with the axial sheath. The axis itself is composed of concentric layers with different 
refraction-index; in the axial lumen the fibrous or cellular intima lies against the horny layers; in 
one case the axis is massive, without axial lumen. — The young spines are massive in several 
species ( Sckizop. apfinis , Bath, patula , Euant. myriophylla) but in other species they are hollow 
and usually club-shaped. This cavity may be in connection with the axial lumen (Euant. dichotoma, 
Stick, variabilis). Probably the young spines originate through an outward folding of the thin 
axial wall; so the diminuition of the diameter of the axial lumen at a greater distance from the 
top may also be explained by this. — The cavity in the spines disappears in a later state, probably 
through the pressure of the surrounding growing layers. The spines loose their club-shape and so 
