SEA-FLOWERS 



477 



One of the commonest British members of the group is the 

 organism to which the unpleasant name of Dead-Mans Fingers 

 {Alcyonium digitatum) is applied, a name justified to some extent 

 by the thick branches of the colony that look something like 

 the swollen fingers of a clumsy hand (fig. 292). In a specimen 

 cast up on the beach the individual polypes will have been drawn 

 back into the fleshy substance of the colony, their position being 

 indicated only by small depressions situated at a little distance 

 from one another. Quite 

 another appearance is pre- 

 sented by a living specimen 

 with all the polypes pro- 

 truded, these having a dis- 

 tinctly flower-like appear- 

 ance, with eight feathery 

 tentacles suggesting petals. 

 As in an anemone, the 

 mouth leads into a gullet, 

 provided in this case, how- 

 ever (as also in some of the 

 anemones), with but one 

 ciliated groove, and united 

 to the body -wall by only 

 eight septa. The digestive 

 cavities of the polypes are 

 continuous with canals which 

 traverse the common flesh. At first there appears to be no 

 skeleton; but microscopic examination reveals the presence of 

 numerous calcareous spicules of characteristic shape, scattered 

 through the comparatively thick supporting layer which comes 

 between the ectoderm and endoderm (see p. 474). There is 

 reason to believe, however, that the spicules have been formed 

 by the activity of ectodermic cells which have become detached 

 from their own layer. 



Another familiar example of the group is the Organ-pipe 

 Coral {Tubipora musicd), in a dried specimen of which may be 

 seen numerous red tubes connected together by " platforms " of 

 similar material at different levels. From these platforms new 

 individuals grow up, and so the coral increases in breadth as it 

 gets older. As in colonial corals generally the individuals are 



iFig. 292. — Dead-Man's Fingers {Alcyotiiutn) 



A, A colony, reduced, ri, Tip of a branch, magnified, showing 

 polypes in different stages of expansion and retraction; mes., a 

 mesentery, c. Cross-section through body of a polype, magnified ; 

 MES., mesenteries (8 in all are present): note the single food-groove 

 in lower side of gullet. 



