SEA-WORMS AND SEA-ANEMONES 81 



The mere sand-flat of the low tide is not a bad 

 hunting ground ; but the rock pools, often exposed when 

 the tide is out, and the fissures in the rocks and the 

 under surfaces of slabs of rock revealed by turning them 

 over — are the greatest sources of varied delight to the 

 sea-shore naturalist. It is well to take a man with you 

 on to these rocks to carry your collecting bottles and 

 cans, and to turn over for you the larger slabs of loose 

 stone, weighing as much as a couple of hundredweight. 

 The most striking and beautiful objects in these rock 

 pools are the sea-anemones (Fig. 6 and Frontispiece). 

 They present themselves as disk-like flowers from I to 5 

 inches in diameter, with narrow-pointed petals of every 

 variety of colour, set in a circle around a coloured centre. 

 The petals are really hollow tentacles distended with sea- 

 water, and when anything falls on to them or touches 

 them they contract and draw together towards the centre. 

 The centre has a transverse opening in it which is the 

 mouth, and leads into a large, soft-walled stomach, separ- 

 ated by its own wall from a second spacious cavity lying 

 between that wall and the body wall, and sending a 

 prolongation into each tentacle. The stomach opens 

 freely at its deep end into this second " surrounding " 

 chamber, which is divided by radiating cross walls into 

 smaller partitions, one corresponding to each tentacle. 

 The nourishing results of digestion, and not the food it- 

 self, pass from the stomach into the subdivided or " sep- 

 tate " second chamber. There is thus only one cavity 

 in the animal, separable into a central and a surrounding 

 portion. 



In this respect — in having only one body cavity — 



sea-anemones and the coral-polyps and the jelly-fishes 



and the tiny freshwater polyp or hydra, and the marine 



compound branching polyps like it — agree with one 



6 



