138 CCELENTERATA OR STINGING- ANIMALS. 



forms are able to shift their position by short stages. They 

 feed on small animals,— Molluscs, Crustaceans, Worms, 

 which are caught and stung by the tentacles, but many 

 must depend largely on minute organisms, while others may 

 be seen trying to engulf molluscs decidedly too large for 

 them. A few anemones, without pigment or with little, 

 have symbiotic Algse in their endoderm-cells ; the bright 

 pigments of many others seem to help iri respiration. 

 Besides the normal sexual reproduction (in which the young 

 are sometimes developed within the parent), some sea- 

 anemones exhibit a power of asexual multiplication by de- 

 taching portions from near the base, and fission occurs in 

 a few forms. 



External Appearance — The cylindrical body is fixed by 

 a broad base ; it bears circles 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. Water may 

 pass out gently or otherwise by a pore at the tip of each 

 tentacle, and long white threads, richly covered with sting- 

 ing-cells, are often ejected by holes on the walls of the body. 

 In certain states, especially if dying, the sea-anemone pro- 

 trudes its gullet and turns itself partially inside out. 



General Structure of the Body. — The Anthozoon polype 

 differs markedly from the hydroid — not only because an 

 invagination from the oral disc inwards has formed a gullet ; 

 but also because a number of partitions or mesenteries 

 extend from the body-wall towards this gullet. Some of 

 the partitions are " complete," 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 is thus divided into a number (some multiple 

 of six) of radial chambers. These are in communication at 

 the base, so that food-particles from the gullet may pass into 

 any of the chambers between the partitions. Moreover, each 

 partition is perforated, not far from the mouth, by a pore, 

 besides which there is often another nearer the body-wall. 

 The tentacles are continuous with the cavities between 

 the mesenteries, and thus all the parts of the body are in 



