PROTOZOA, CCELENTERA, AND ECHINODEEMA 98 



occur only in the abyss exhibit some curious modifi- 

 cations. The manner in which the tentacular pores 

 have become enlarged, and the tentacles themselves 

 diminished in size and flexibility, has already been 

 referred to in a previous chapter (p. 36). 



The family of sea anemones that has been named 

 the Corallimorphidae, characterised by the stiffness 

 and slight contractility of the body, the knobbed 

 nature of the tentacles, and their distribution in 

 several series, was, until quite recently, considered to 

 be a true abysmal family. The two species, Coralli- 

 morphus rigidus and C. profundus, are known to occur 

 only in very deep waters, and present some curious 

 modifications of structure in relation to their habit ; 

 but it seems probable that to this family should 

 be added the remarkable littoral form Thelaceros 

 rhizophoi'ci' found on the coast of Celebes attached 

 to the roots of the mangrove trees in the swamps. 



The fact that all the principal groups of the 

 Actiniaria, except, perhaps, the group that includes 

 those forms with only eight mesenteries, the Edwardsise, 

 have representative genera or species in the great 

 depths of the ocean, points to the conclusion that the 

 sea anemones have migrated from the shallow waters 

 in comparatively recent times, and that the migra- 



