24 A Guide to the Zoological Collections in the 



attached at its aboral pole, which is known as the pedal disk 

 or foot-plate, and provided with a mouth and crown of hol- 

 low tentacles at the oral pole, which is known as the oral 

 disk or peristome. In Polysiphoma, a deep-sea form, 

 shown in the Case, the tentacles are reduced to short broad 

 stumps, each of which has an orifice at the end through 

 which water with nutrient particles can enter the gastric 

 cavity. The hollow of the tube forms the stomach, into 

 which the pendent oesophagus opens, as may be seen in 

 the several longitudinal bisections of Sphenopiis. The wall 

 of the stomach is raised to form sarco-septa or mesenteric 

 folds, to the free edges of which are attached bunches of 

 filaments (mesenteric filaments) and acontia. The latter 

 are freely armed with stinging-cells, and can be protruded 

 rapidly from the mouth, and sometimes through the body- 

 wall, in defence, when the sea-anemone is irritated. From 

 the free edges of the mesenteric folds the reproductive or- 

 gans also arise. The sarco-septa, or mesenteric folds, with 

 their bunches of mesenteric filaments and of generative 

 products are very clearly displayed in the longitudinal 

 bisections of Sphenopiis and Cerianthus. The acontia are 

 beautifully seen in ,the longitudinal bisection of Cerian- 

 thus, fringing the lower end of the septa. 



The tentacles in the Actiniaria are multiples of six : 

 they are usually retractile, as is seen in the sections of 

 Sphenopus, and their function is to seize upon prey and 

 convey it to the mouth. 



Most of the sea-anemones have soft bodies, but some, 

 as in the exhibited specimens of Sphenopus arenaceus and 

 Sphenopus marsupiaiis, and oiZoanthus and Episoanthus, 

 have a leathery external coat, which is further strengthened 

 by a layer of sand-grains agglutinated together. The 

 interesting form Cerianthus, too, some large specimens of 

 which are to be seen in the Case, is furnished with a thick 

 jacket made of mucus and mud and sand, into which the 

 animal can retract itself. 



Most of the sea-anemones are simple, that is to say 



