The Sea-anemone has the form of a cylinder, the height of which slightly
exceeds the diameter. The cylinder or column is fixed by its broad base. At
the free end the column passes into a horizontal plate, the disc or peristome. In
the middle of the disc is the slightly elevated slit-like mouth. Arising from the
disc, and encircling the mouth, are numerous short tentacles regularly arranged
in circles. There is a pore at the tip of each tentacle through which water may
be passed.
Directive mesentery Genital organ Mesenteric filament
f 3 ‘
restierereservoma Longitudinal muscle ‘ /


~Tertiary-” :
-mesentery a9 %


‘5 Se?
real B.
‘
eo |
~" Primary mesentery


Siphonoglyph


Fic. 12.—A. Transverse Section through the gullet region (stomodzum) of a Sea-
anemone ; B. Transverse Section below the gullet, about the position indicated by
the arrow in Fig. 13, A.
General Structure (Transverse Section).
If a transverse section is made across the column a short way below the
tentacles the following structures will be seen :—


(a) The body-wall, composed of ectoderm, mesogloea and endoderm.
(i) The ectoderm consists chiefly of ciliated, sensory, stinging and
gland cells, and also of numerous muscle cells.
(ii) The mesogloea is a tough and fairly thick supporting tissue
between the ectoderm and endoderm, and it forms the basis for
their cells. It contains amceboid cells which have wandered
into it from the ectoderm chiefly ; it is therefore mesenchyme
tissue or incipient mesoderm.
(iii) The endoderm consists mainly of flagellate cells, with muscular
fibres at their roots.
