SCRUPOCELLARIA REPTANS. 55 



there are always, as far as I have seen, seven or five cells; on 

 the larger internode there are three pedunculate avicularia, 

 on the smaller two. The peduncle on which these appen- 

 dages are mounted is much elevated ; it is swollen at the 

 base, and higher in front than behind, so that the avicu- 

 larium is tilted up, its strongly curved beak being directed 

 outwards. 



The operculum, which in its earliest stage of growth is 

 simple and entire, becomes dicliotomously branched, and 

 spreads out like an antler over the entire aperture, which 

 it completely protects. 



The radical fibres are present under two forms, and 

 enable the species to adapt itself to very different habi- 

 tats. In one they are simple tubes, originating, as all 

 similar appendages do in this group, at the base of the 

 vibracular cell ; and from the free extremity a number of 

 fibrils are given off, which branch and anastomose and 

 form circular reticulated disks, by which the polyzoon 

 is firmly attached to the surface of the rock or the frond 

 of the sea-weed. These disks may remind us o£ the 

 rootlets by which the ivy clings to its support. The 

 tubes are not merely produced towards the base of the 

 zoarium, but along the course of the branches, which, as 

 they increase in length, are firmly attached at intervals ; 

 and in this way the polyzoon creeps, like a plant, over 

 the surface on which it grows. But a modification of 

 the merely adherent appendage is also met with; and it 

 would seem that the particular form which the radical 

 fibre assumes is very much determined by the nature of 

 the base on which the polyzoon is developed. In its 

 second form, the fibre is covered for about two thirds of 

 its length with sharp, recurved, hook-like processes, and 

 is converted into an admirable prehensile organ. It is 

 a veritable grapnel, which is plunged into the soft sar- 



