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 mouth 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 (planule). 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- 
