SEA-ANEMONES 143 



may be, has a corresponding chamber. The inner sac has a mouth, 

 like a slit, at the top of the disk, opening to the outside, and it 

 also has openings into the chambered spaces which surround it. 

 These chambers also open into the hollow tentacles ; thus a con- 

 tinuous circulation throughout the whole animal is established. 



The food taken in at the mouth is digested in the inner sac, 

 passes through all the chambers of the cavity as nutritive fluid, and 

 is then expelled at the month again. The inner sac, or gullet, has 

 longitudinal grooves ; two of these are broad and deep, and corre- 

 spond to the corners of the mouth. These are called siphonoglyphs. 

 The sea-anemone is soft and contractile, and belongs to the only 

 order of this class which does not secrete a skeleton. It has two 

 sets of muscles, one of which extends from the base to the sum- 

 mit of the body and is placed on the dividing partitions. Sea- 

 anemones are classified by the arrangement of the septa and the 

 manner in which the muscles are placed upon them. The other 

 set of muscles is arranged around the circumference of the col- 

 umn or body. Each tentacle is furnished with similar sets of 

 muscles. The animal is sensitive, and at the least alarm con- 

 tracts its body by means of these muscles, and quickly trans- 

 forms itself from a beautiful, flower-like form into a shapeless, 

 unattractive, inconspicuous mass. 



The Actiniaria are developed from the egg. The eggs form 

 on the edges of the inner walls (mesenteries), and when mature 

 drop into the outer sac (gullet), and out of the mouth as ciliated 

 spheres (planulse). After swimming about for a time these at- 

 tach themselves to rocks, and, conforming to the irregularities of 

 the surface, secure a tight hold. The upper surface of the 

 planula then becomes depressed and forms a gullet, and in time a 

 complete animal is formed. The Actiniaria reproduce also by 

 budding. A small protuberance or simple elevation of the body- 

 wall appears on the side at the base, or in some species on the 

 disk of the animal, which generally develops into a complete 

 animal and at maturity falls away from the parent. Sometimes 

 several anemones bud simultaneously from the same individual, 

 and a third generation commences to bud at the same time from 

 the immature young of the parent stock. The sea-anemones in- 



