ANNELIDES. 



79 



in some genera, tentacular cirri from their similarity to the tentacula 

 on the sides of the head. They are simple, soft, tapered filaments 

 or papillary processes attached to the dorsal and ventral lobes of 

 the foot, at or near the base. Their office appears to be tactile. 



The Foot, properly so-called, is the papillary process, tubercle, or 

 fold in which the Bristles are sheathed. When the process is single 

 and undivided, the foot is said to No. V. 



be uniramous ; when it is divided 

 into two lobes, it is biramous 

 (No. V. fig. 12). The upper 

 division is called the dorsal 

 branch, and the inferior the ven- 

 tral branch. They are more or 

 less apart, — sometimes so near as 

 to coalesce, and not to be distin- 

 guished from the uniramous ex- 

 cepting by the presence of two 

 bundles of bristles, — sometimes 

 so wide asunder that they seem 

 to have no connexion. Of the 

 latter the foot of the Nephthys 

 is a good example (fig. 12). In 

 this figure dfis the dorsal branch, 

 and vf the ventral branch armed 

 with their long bristles ; I are the 

 compressed lamellae attached to the foot ; br are presumed to be the 

 branchiae ; and c is the inferior cirrus ; and, in this species {N. longise- 

 tosa), there is no superior cirrus. This interpretation of the organs 

 appears to me erroneous. The function of the sickle-shaped process is 

 entirely conjectural ; and surely the compressed lamellae are branchial, 

 although undoubtedly the function is not confined to them. 



Bristles. — There are four kinds of bristles connected with the feet, 

 viz. the Spine, the Spinet, the Bristles properly so called, and the 

 Booklets. Other bristles which belong to the body will be noticed 

 under the genera in which they occur. 



1. The Spine (Plate III. fig. 1) is subulate and straight, tapering 

 insensibly from the base to the point. It is always associated with 

 the bristles, there being one, or at most two, in the centre of each 

 fascicle ; and it is readily distinguished by being stouter and dark- 

 coloured. It is not protrusile. Audouin and Milne-Edwards say that 

 the base is placed in the bowl of a little cup ; but certainly this is not 

 usually the case. The basal portion is lighter-coloured than the upper. 



2. The Spinet is not in general so stout as the spine, neither is it 

 dark-coloured. It is found only on a few feet in some genera, and 

 in most is absent. It is associated with the bristles, and is known 

 by being stiffer and stouter, and different in shape. The apex is 

 forcipate (PL III. fig. 2), or forked (figs. 3, 3*, 4, 5). 



3. The Bristles are simple or compound. 



The simple Bristle is formed of a single continuous piece. It is 

 always fasciculate. It varies much in strength and size and figure ; 



