COMPOSITE HYBROZOA — TUBULABID^. 463 



like the stalks of wheat, upon the base to which they are attached. 

 This beautiful zoophyte, which sometimes grows between the 

 tide-marks^ but is more abundantly obtained by dredging in 

 deep water, often attains a size which renders it scarcely a micro- 

 scopic object; its stems 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 ex- 

 pelled 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 fore- 

 going 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 Chara (§ 201). The Ee- 

 productive process in this family seems to be efiected 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 tree-like structure, froiji three to six inches 

 high, is thus formed. But around the polype-heads are evolved 

 gemmse of a different kind, as in Coryne ; these being capsules, 

 within which are formed either one or several ovoid bodies, that 

 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. Whether this is a method of producing free gemmse, or 

 whether it is a process of sexual generation, is not yet certainly 

 known ; no spermatozoa have been observed in any of these 

 ciapsules ; and if none should be detected by careful search, the 

 polypes thus evolved may be presumed to be buds. In several 

 Tubularidse, the evolution of free Medusa-like buds, resembling 

 those of Syncoryne (Fig. 222), has been observed ; and all ana- 

 logy would indicate that they act as the sexual organs, the de- 

 velopment of spermatozoa in some, and of ova in others, probably 

 not taking place until after they have led an independent life 

 for some time. It is worthy of mention here, that when a Tu- 

 bularia 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 re- 

 generation may take place many times in the same individual. 



304. It is in the families Oampanularidce and Sertularidoe, that 

 the horny polypary attains its completest development ; since it 



