STRUCTURE OF SEA-ANEMONES. 



29 



soak ia it for two or three days until tlie tissues become hard enough 

 to cut well. Then vertical and transverse sections may be made with 

 a sharp knife. The first fact to ob erve is, tliat an alimentary canal 

 is much more clearly indicated than in the llydrozoa, 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, tliere is a mass of long coiled 

 filaments, the mesenterial filaments (Fig. 30, cr), which contain lasso- 

 cells, in dissecting the sea-anemone tliese mesenteria' filaments are 

 always more or less in the way, and have to be carefully removed so 

 as to expose the ovaries and adjoining parts. Tliey press out of the 

 mouth and ci.icUdes (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 tlie 

 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 

 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 direct'y with 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 tliese 

 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 



Fro. 30. — Partly diagrammatic 

 sketcli of the anatomy of an 

 Actinia {Metridiuvi) with the 

 tentacles disproportionately 

 enlarged. s.npsonhnsrn'irT?'. mi^- 

 senteries, or septa; o. ovary; ci, 

 cinclides; cr, mesenterial fila- 

 ments; e, eyes; op, orifice 

 through the septa. 



