Radical Fibres of tlie Polyzoa, 219 



scritposa ; but I have long been aAvare that they enter into 

 the history of another member of the same genus, the common 

 Scrujiocellaria reptans'^ of authors. I will insert here the 

 passage relating to this subject which I had prepared for my 

 forthcoming ' History of the British Marine Polyzoa.' It is 

 taken from the account of Scrupocellaria reptans : — " The 

 radical fibres are present under two forms, and enable the 

 species to adapt itself to very different habitats. 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 oif, that anastomose 

 and form circular reticulated disks, by which the polyzoon is 

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

 seaweed. These disks may remind us of the rootlets by which 

 the ivy clings to its support. The radical tubes are not merely 

 produced towards the base of the zoarium, but along the 

 course of the brandies, which, as they increase in length, are 

 firmly attached by them 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 it is covered for about two thirds of its 

 length with sharp, recurved, hook-like processes, and is con- 

 verted into an admirable prehensile organ. It is now a veri- 

 table grapnel, by means of which the polyzoon can lay firm 

 hold of the stems of zoophytes or the more delicate algse, or, 

 plunging it into the soft sarcode, find a safe home upon the 

 sponge. Dredging on one occasion in Salcombe Bay I took 

 up a piece of some cotton material which was overgrown by 

 S. reptans. On the uneven fibrous surface the adhesive disks 

 would have been almost useless ; a few only were developed ; 

 but the toothed processes were present in profusion, and had 

 worked their way in amongst the threads of the fabric, which 

 had become entangled about the hooks, and so anchored the 

 tufts securely. On a specimen beside me, growing on the flat 

 surface of a Laminaria-hondi^ I can find not a single grapnel ; 

 but the disks are finely developed and of large size." 



In Cellularia plumosa we meet with another interesting 

 modification of the radical fibres. In this species they occur 



* I liave restored this species to the genus Scrupocellaria, instead of re- 

 ferring it with Busk to the Canda of Lamouroux, because it is furnished 

 with the lateral avicularia which are characteristic of the former genus. 

 They are small and feebly developed, and have hitherto escaped observa- 

 tion ; but they exist. 



