76 



ZOOLOGY. 



body-walls), not always present, and end of the tentacles, 

 and thus come in contact with animals forming their food. 

 The ovaries and spermaries can be distinguished by their 

 forming masses of closely convoluted tubes much thicker 

 than the mesenterial filaments, and situated on the outside 

 next to the free edge of each mesentery ; they are also of a 

 pale lilac tint in Metridium marginatum (Fig. 50, o). They 

 are not easily distinguishable from each other by the naked 

 eye. The figure shows at the base of the body the free 

 edges of the mesenteries (m) of different heights, with the 

 spaces between them through which the chyme passes into 



the body-cavity. For the com- 

 plete passage of the circulating 

 fluid the six primary mesenteries 

 are perforated by a large orifice 

 {op) more or less oval or kidney- 

 shaped in outline (Fig. 50). The 

 digestive sac is divided into two 

 divisions, the mouth and stomach 

 proper, the latter when the ani- 

 mal is contracted being much 

 shortened, and with the walls 

 vertically folded, as seen in the 

 cut. 



In the tentacles are lodged the 

 lasso-cells or nematocysts, and 

 the tentacles are hollow, com- 

 municating directly with a cham- 

 ber or space between the mesen- 

 teries, and are open at the end. When a passing shrimp, 

 small fish, or worm comes in contact with these tentacles, 

 the lasso-cells are thrown out, the victim is paraly.-ied, 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 tegument of the animals which may 

 be swallowed by the Actinia are rejected from tlie mouth 

 after the soft parts are digested. Pigment-cells, which are 





1 



Fig. 50. — Partly diagrammatic 

 sketch of the anatomy of an Actinia 

 {^etridivm) with the tentacles dis- 

 proportionately enlarged, s, stom- 

 ach ; ffi, mesenteries, or septa ; o, 

 ovary ; ci, cinclis ; cr, mesenterial 

 filaments; e, eyes; op, orifice through 

 the septa.— Drawn Dy J. S. Kingeley, 

 under the author's direction. 



