540 TUBULARID.E l CAMPANULARIDiE : SERTULARIDCE. 



being sometimes no less than a foot in height and a line in diameter. 

 Several curious phenomena, however, are brought into view by 

 Microscopic examination. The Polype-stomach is connected with 

 the cavity of the Stem by a circular opening, which is surrounded 

 by a sphincter; and an alternate movement of dilatation and 

 contraction takes-place in it, fluid being apparently forced-up from 

 below, and then expelled again, after which the sphincter closes in 

 preparation for a recurrence of the operation ; this, as observed 

 by Mr. Lister, being repeated at intervals of eighty seconds. 

 Besides the foregoing movement, a regular flow of fluid, carrying 

 with it solid particles of various sizes, may be observed along the 

 whole length of the Stem, passing in a somewhat spiral direction, 

 and a good deal resembling the rotation in Ohara (§ 254). 



416. The Reproductive process in this Family seems to be effected 

 in various modes; and the true relation between them has not yet been 

 clearly made-out. The Polype-stem sometimes puts-forth branches, 

 at the termination of which new Polypes ultimately make their 

 appearance, as in other Composite Hydrozoa ; and in the genus 

 Eudendrium, which is found on many parts of our coasts attached 

 to old shells or stones dredged- up from deep water, a beautiful 

 arborescent fabric from three to six inches high is thus formed. 

 But around the Polype-heads in Tubular ia indivisa are evolved 

 Gemmae of a different kind, which, like those of Coryne, have 

 a Medusoid character, but do not detach themselves from the 

 stem ; within each of these are formed two ovoid bodies, which 

 begin to develope themselves into the polype-form even before their 

 escape from their containing cases, and soon fix themselves after 

 their immersion, shooting-up into stems like those of the parent. 

 In several Tubularidse, however, the evolution of free Medusa-like 

 buds, resembling those of Syncoryne (Fig. 276), has been ob- 

 served. — It is worthy of mention here, that when a Tubularia is 

 kept in confinement, the Polype-heads almost always drop-off after 

 a few days, but are soon renewed again by a new growth from the 

 stem beneath ; and this exuviation and regeneration may take 

 place many times in the same individual. 



417. It is in the Families Campanularida and Sertularidce 

 (commonly known as 'Corallines') that the horny Polypary 

 attains its completest development ; not only affording an in- 

 vestment to the Stem, but forming cups or Cells for the protection 

 of the polypes, as well as Capsules for that of the reproductive 

 bodies. In the Oampanularidce the Polype -cells are campanu- 

 late or bell-shaped, and are borne at the extremities of ringed- 

 stalks (Plate xx., c) ; in the Sertularidce, on the other hand, the 

 Polype-cells lie along the stem and branches, attached either to 

 one side only, or to both sides (Fig. 277). In both, the general 

 structure of the individual Polypes (Plate xx., d) closely corre- 

 sponds with that of the Hydra ; and the mode in which they 

 obtain their food is essentially the same. Of the products of 



