SEA-LILIES AND FEATHER-STARS 



461 



joined end to end. At regular intervals the stalk bears circlets 

 of jointed filaments {cirri) which also are strengthened by a 

 deposit of lime. 



The internal structure is very complex, and it need only be 

 said that the gut does not extend into the arms, and that apart 

 from it the chief organs 

 have the radial arrange- 

 ment described for 

 other types. 



Although Sea- Lilies 

 are distinctly scarce 

 animals, the same can 

 scarcely be said for the 

 Feather- Stars, of which 

 one kind {Antedon or 

 Comatula rosacea) (fig. 

 283) is not uncommon 

 in British seas. Its 

 life -history is one of 

 peculiar interest, for 

 the eggs develop into 

 a stalked larva which 

 is found attached to 

 sea -weed, and looks 

 like a minute Sea- Lily 

 (fig. 284). Later on, 

 the stalk disappears 

 and the animal takes 

 to a free life, though 

 it is possessed through- 

 out its existence of a circlet of cirri, corresponding to the top 

 circlet of those structures in a stalked form, and used to anchor 

 the creature, and also in climbing. The life-history is interesting, 

 chiefly because it is one of the best-known examples of a case 

 where the development of the individual is a compressed present- 

 ment of the genealogy of the species. If the Feather-Star were 

 the only known Crinoid there would be a strong presumption that 

 its remote ancestors were stalked, and this conclusion is fully 

 borne out by a study of recent and fossil forms. 



Fig. 284. — Stages in development of Feather-Star {Comatula), mucl' 

 enlarged. 3 is the stalked or pentacrinus stage 



