122 THE AQUARIAN NATURALIST. 







than the larger number mentioned, thus giving 6000 

 polyps as the tenantry of a single polypidom ! Now, 

 many such specimens, all united too by one common 

 fibre, and all the offshoots of one common parent, are 

 often located on one sea-weed the site then of a 

 population which neither London nor Pekin can rival. 

 But Plumularia cristata is a small species, and there 

 are single specimens of Plumularia falcata or Sertu- 

 laria argentea to be met with in equal abundance, of 

 which the family may consist of 80,000 or 100,000 

 individuals. Such are the " insect millions peopling 

 every wave." 



The extremities of the stems of the TUBULARI^ 

 described in a preceding chapter are simply cylin- 

 drical, and unprovided with any cavity into which the 

 terminal Hydras can be withdrawn. But the extremi- 

 ties of the SERTULARI.E present cup-like cells, and a 

 multitude of similar cells are implanted on the stem, 

 boughs and branches, of various configuration in dif- 

 ferent species, into which the hydriform polyps can 

 retreat for shelter. Some of these cells are little more 

 than a simple orifice ; some resemble a tooth, a cup, 

 a flask or a bell with a smooth or serrated lip. Some 

 are armed with a longer or shorter spine, or the 

 margin of others is guarded by several extraordinary 

 processes, extending in straight lines, or in curvatures 

 of inordinate length. These cells, with their tenants, 

 stand on one or both sides, or are arranged around 

 the central stems. They may be placed singly, at 

 distant intervals, in pairs or in clusters, either crowded 

 together or far apart. Sometimes they are seated on 

 stalks or branches, or twigs, jointed, whorled or frilled ; 



