CHAPTER XIX 

 THE SEA- ANEMONE AND SOME ALLIES: OELENTERA 



To-day the many-hued anemone 

 Waving, expands within the rock-pools green, 

 And swift, transparent creatures of the sea 

 Dart throu' the feathery sea-fronds scarcely seen. 



SIR LEWIS MORRIS. 



The Sea-Anemone. The best-known sea-anemone of the 

 North Atlantic coast is Metrid'ium margina'tum (Figs. 126, 

 128, and 129). Although this species is usually found in tide- 

 pools, it also lives attached to the piles of wharves in har- 

 bors where the impurities of the water are not too great. 

 The picture of the tide-pool shows sea-anemones in various 

 attitudes. Metridium has the power of moving, by creeping 

 along on its base, but it seldom changes its place of attach- 

 ment, even in the coldest weather. 



The form of Metridium is nearly cylindrical. The base, 

 which is the aboral surface of the animal, widens irregularly 

 to fit the surface of attachment, thus enabling the body to 

 maintain its hold by expelling the water from beneath the 

 disk. The oral end of the column-shaped body expands into 

 a crown of many small, slender tentacles. At the middle of 

 the oral surface is the mouth. The skin of the body is soft, 

 but rather tough. An animal with the general plan of struc- 

 ture of. the sea-anemone is called & polyp.. 



The food of the sea-anemone consists in general of many 

 kinds of microscopic pelagic organisms. The capture of 

 prey is accomplished by a method peculiar to the phylum to 

 which Metridium belongs. All over the tentacles are number- 

 less microscopic cells containing nettling -capsules (compare 



252 



