90 



ANNELIDES. 



and of the base or cupule (5). When the spine is forcibly torn 

 away from its sheath, the cupule is detached, and remains adherent 

 to the fascicle of muscular fibres in which it is implanted. 



The Bristles are much varied. They may be divided in the first 

 place into the simple and compound*. 



The simple bristles (No. XIII. fig. 12-21) are formed of a single 

 piece only ; or if any are composed of several pieces, these are all 

 of the same kind, and superadded to one another like the articula- 

 tions of the filiform or setaceous antennae of certain insects, or rather 

 like the joints of a Conferva (fig. 12). 



The form of the simple bristle is very variable. Some terminate 

 in a more or less sharp point, either cutting, denticulated, or forked 

 (figs. 13, 14) ; others are obtuse and rounded, or even enlarged at 

 the extremity (figs. 15, 16). Some are of such extreme fineness, 

 that they may more properly be called hairs than bristles (fig. 1 1), 



No. XIII. 



Such are the beautifully coloured metallic and iridescent hairs which 

 garnish the sides and feet of the Aphrodites ; and in some species of 

 this genus a portion of these long hairs is interlaced so as to form a 

 sort of felted membrane to cover the scales and branchiae, and pro- 

 tect them from injury. But the utility of such hairs, in other 

 respects, is of a passive kind : — they may make the worm trouble- 

 some to the palate of a foe, but they cannot be directed against that 



* The figures of Oersted in pi. 1 of his ' Annul. Dan. Consp.' are excellent. 



