iv PHYLUM CCELENTERATA 125 



being small and very numerous, that the most complex 

 of all Corals, the Madrepores {Fig. 60, B\ are produced. 



The Actinozoa are remarkable for the variety and brilli- 

 ancy of their colour during life. Every one must have 

 noticed the vivid and varied tints of Sea-anemones ; but in 

 life the corals also exhibit a marvellously varied and gorge- 

 ous colouring ; and the same holds good of many of the 

 Alcyonaria. 



Many Actinozoa, like many Sponges (p. 89), furnish 

 examples of commensalism, a term used for a mutually 

 beneficial association of two organisms of a less intimate 

 nature than occurs in symbiosis. An interesting example 

 is furnished by the Sea-anemone Adamsia palliata. This 

 species is always found on a univalve shell such as that of 

 a Whelk inhabited by a Hermit-crab. The Sea-anemone 

 is carried from place to place by the Hermit-crab, and in 

 this way secures a more varied and abundant food-supply 

 than would fall to its lot if it remained in one place. On 

 the other hand, the Hermit-crab is protected from the 

 attack of predacious fishes by retreating into its shell and 

 leaving exposed the Sea-anemone, which, owing to its 

 toughness, and to the pain caused by its poisonous stinging- 

 capsules, is usually avoided as an article of food. 



4, THE CTENOPHORA 



The Ctenophora or Comb-jellies are a group of free- 

 swimming, gelatinous, transparent animals which occur, some- 

 times in enormous numbers, in the surface waters of the sea. 

 Theanimal(Fig. 6i)has the appearence of a mass of clear jelly, 

 usually of a globular shape ; and no pulsating movements, such 

 as those by means of which a Medusa propels itself, are to 

 be observed, Running over the surface, nearly from pole to 



