30 



NATURAL HISTORY. 



ening the body, then unrolling the free end, from which it soon protrudes 

 a large number of long, tapering tentacles, in the centre of which is the 

 slit-like mouth. Inside of the body is a sac open at the lower end, which 

 serves as a stomach, while from the periphery of the body to this stomach 

 run a number (six) of partitions. The whole may roughly be compared to 

 a wheel, the stomach being the hub, the partitions the spokes, while the 

 outer body wall is the rim and tire. Between these six principal parti- 

 tions are others which do not reach to the stomach. The whole object of 

 this complexity of structure seems to be to gain additional digestive and 

 absorptive surface. In the higher animals, as is well known, the products 

 of digestion are carried by the blood to the various organs which need 



Fig. 30. — A fully expanded sea-anemone (Crambactis arabica). 



nourishment ; but here there is no blood, no heart, no organs of circulation. 

 Each part of the body picks out the nourishment it needs from the par- 

 tially digested mass. 



The habits of a few species of anemones may be mentioned. Most 

 of them live attached to submerged objects ; but while most of these are 

 usually found on stones, etc., a few prefer a living anchorage. Thus, in 

 the Eastern seas there is one species which goes about on the back of a 

 crab, and it is stated that neither is found without the other. On our 

 own coast there are similar relationships.' Here it is a hermit crab that 

 is utilized by the anemone, which settles down on the shell occupied by the 

 interesting crustacean. Usually hermits have to change their houses with 

 growth, — a feature to be referred to again; but the hermit with this 



