STBUGTURE OF SEA-ANEM0NE8. 
29 
soak in it for two or three days until the tissues become hard enough 
to cut well. Then vertical and transverse sections maybe made with 
a sharp knife. The first fact to ob.^erve is, that an alimentary canal 
is much more clearly indicated than in the Hydrozoa, there being a dis- 
tinct digestive sac, separate from the body-walls, hanging suspended 
from the mouth-opening, and held in place by six partitions {mesen- 
teries), which divide the body- cavity into a number of chambers. 
The digestive sac is not closed, but is open at the bottom of the body, 
connecting directly with the chambers, so that the chyme, or prod- 
uct of digestion, passes down to the floor of the body, and then into 
each of the chambers. On the free edges of the shorter mesenteries, 
which do not extend out to the stomach, there is a mass of long coiled 
filaments, the mesenterial filaments (Fig. 30, cr), which contain lasso- 
cells. In dissecting the sea-anemone these mesenterial filaments are 
always more or less in the way, and have to be carefully removed so 
as to expose the ovaries and adjoining parts. They press out of the 
mouth and cinclides {ci, small openings through the body-walls), not 
always present, and end of the tenta- 
cles, and thus come in contact with 
animals forming their food. The fig- 
ure shows at the base of the body the 
free edges of the mesenteries (m) of 
different heights, with the spaces be- 
tween them through which the chyme 
passes into the body-cavity. For the 
complete passage of the circulating 
fluid the six primary mesenteries are 
perforated by a large orifice {op) more 
or less oval or kidney-shaped in out- 
line (Fig. 30). The digestive sac is di- 
vided into two divisions, the throat 
and stomach proper, the latter when Fig. 
the animal is contracted being much 
shortened, and with the walls verti- 
cally folded, as seen in the cut. 
In the tentacles are lodged the lasso- 
cells, and the tentacles are hollow, 
communicating directly wiih a cham- 
ber or space between the mesenteries, and are open at the end. When 
a passing shrimp, small fish, or worm comes in contact with these 
tentacles, the lasso-threads are thrown out, the victim is paralyzed, 
other tentacles assist in dragging it into the distensible mouth, where 
it is partly digested, and the process is completed in the second or 
lower division of the digestive canal. The bones, shells, or hard 
30. — Partly diagrammatic 
sketch of the anatomy of an 
Actinia (Metridium) with the 
tentacles disproportionately 
enlarged, s. oesophagus; m, me- 
senteries, or septa; o, ovary; ci, 
cinclides; cr, mesenterial fila- 
ments; e, eyes; op, orifice 
through the septa. 
