120 SERTULARI.E. 



the club-shaped knob at the end of the branches a head, 

 it in fact contains the whole proper body of the Polype, 

 the substance which fills the tube being merely a me- 

 dulla common to all. The flexibility of the branches, 

 and their perfect union with the base of the head, en- 

 able the animal to move the latter part in every direc- 

 tion. Besides this, it can shorten or lengthen the head 

 at pleasure, protruding the mouth, and bending it round 

 to catch any object of prey. Its motions, which are 

 slow, and not ungraceful in their delibei*ation, may 

 readily be watched in a small vessel of sea-water, and 

 specimens may be found on almost any rocky shore. 



Of the restricted genus Sertularia, seventeen British 

 species are known, many of which are only found in deep 

 water. I shall take as an example S. filicula, a common 

 but elegant species, found on sea-weeds near low-water- 

 mark, especially at the root of the large Oar-weed, and 

 often thrown up along the shore. The Sertularice are 

 of a horny colour and texture, branched like plants, 

 sometimes forked, but very generally feathered or pin- 

 nate. Their branches are toothed ; and, when mag- 

 nified, are found to consist of a single tube, jointed at 

 intervals, and bearing along its sides prominent cells, 

 alternate, or in opposite pairs, one placed at each side of 

 the branch. In some species they are close together, 

 and very distant in others. In these cells, which are 

 hollow, and open at the end, the Polypes reside. When 

 expanded, they show a mouth surrounded by several 

 radiating tentacula ; but they can withdraw themselves 

 at pleasure within the narrow walls of their cell. Besides 

 the cells in which the Polypes reside, most Sertularice 



