192 



PHVLtJM CCELENTERA 



External appearance of a fixed Anemone. ^ — The 



cylindrical body is fixed by a broad base ; it bears whorls 

 of hollow tentacles around the oral disc ; the mouth is 

 usually a longitudinal slit. The tentacles are contracted 

 when the animal is irritated, and the whole body can be 



much reduced in size. 

 Just below the margin 

 of the oral disc there is 

 a powerful sphincter 

 muscle ; this contracts, 

 and pulls together the 

 body wall over the 

 mouth and retracted 

 tentacles. Water may 

 pass out gently or other- 

 wise by a pore at the 

 tip of each tentacle, and 

 long white threads, richly 

 covered with stinging 

 cells, can be ejected in 

 many anemones through 

 the walls of the body 



(Fig. 99)- 



General structure.- — 

 The Anthozoon polyp 

 differs markedly from 

 the Hydroid polyp — not 

 only because an in- 

 vagination from the oral 

 disc inwards has formed 

 a gullet tube, which 

 hangs down into the 



Fig. 99. — Vertical section of a sea- 

 anemone. — After Andres. 



/., Tentacles ; o., mouth ; oes., oesophagus ; 

 c, c'., apertures through a mesentery ; a., a'., 

 acontia ; g., genital organs on mesentery ; 

 m.f., mesenteric filaments ; jn.l., longitudinal 

 muscles ; s., primary septum or mesentery ; 



tCbasarS'"^^'™' ^"•' t^^t^^-^y ^^Pt""^ ; general cavity, but also 



because a number of 

 partitions or mesenteries extend from the body w^all 

 towards this gullet. Some of the partitions are " com- 

 plete," i.e. they reach the gullet ; others are " incomplete," 

 i.e. do not extend so far inwards. The complete 

 mesenteries are attached to the oral disc above, to the side 

 of the gullet, and to the base, and all the mesenteries are 

 ingrowths of the body wall. The cavity of the anemone 



