160 PHYLUM CCELENTERA. 



sometimes developed within the parent), some sea-anemones 

 also multiply asexually by detaching portions from near the 

 base, and fission occurs in a few forms. 



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, 



FIG. 78. External appearance of Tealia crassicorriis. 



and pulls together the body wall over the mouth and 

 retracted tentacles. Water may pass out gently or 

 otherwise 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. 79)- 



General structure. The Anthozoon polyp differs 

 markedly from the Hydroid polyp not only because an 

 imagination from the oral disc inwards has formed a gullet 

 tube, which hangs down into the general cavity, but also 

 because a number of partitions or mesenteries extend from 

 the body wall towards this gullet. Some of the partitions 

 are "complete," t.e. they reach the gullet; others are "in- 



