STYLARIOIDES PLUMOSA. 93 



The perivisceral cavity is divided into two parts by a vertical partition, as Otto 

 found in Flabelligera. 



The anterior opening in a partially contracted example is a vertical slit more or less 

 widened in the centre according to circumstances, and having a frilled margin surrounded 

 by an area with longer papillae which form a fringe. On each side is a vertical ridge, 

 slightly divided into a dorsal and a ventral division, and from each of these springs a 

 remarkably long tuft of golden bristles (Plate LXXXIX, fig. 1), which stretch far in 

 front of the animal and refract the light beautifully. All are boldly articulated, but not 

 quite uniformly so, some, even in the same bristle, being broader than long, and others 

 the reverse. The majority of the divisions seem to have a longer vertical than trans- 

 verse diameter, though the larger bristles usually show shorter segments toward the 

 base. These bristles gradually taper almost from the base to the finely pointed tip which 

 has shorter articulations. Toward the base (in the tissues) the bristle is slightly narrowed, 

 and the transverse articulations are closer and less regular, almost disappearing at the 

 end (Plate CIV, fig. 1 b), and the inserted portion of each bristle is great, no less than a 

 quarter of the length in the longer forms and more in the shorter. From the direction 

 (upward and forward) of these bristles they could be of little use to the annelid on a 

 flat surface, but they would act on the wall of a tube or tunnel, as well as protect the 

 branchiae and palpi. They are comparatively brittle. Numerous parasitic growths, such 

 as pale Fungi, which stretch in a pinnate manner from the shaft and tip, thecate Infusoria, 

 and Vorticellae, abound on them. The next segment likewise has two long tufts of similar 

 bristles, only they are somewhat shorter than the first ; and so with the third segment, 

 the bristles of the latter being considerably shorter than those of the second, especially the 

 ventral group. The fourth segment inaugurates the condition present throughout the rest 

 of the body, viz. a dorsal tuft of the resplendent tapering articulated bristles, now com- 

 paratively short, which spreads in a fan-like manner over the dorsum, and a ventral series 

 of stout spines with a double curve. It occasionally happens that in a mutilated specimen 

 some of these dorsal tufts in the middle of the body are abraded to a level with the skin. 

 The base of the ventral hook is inserted deeply into the tissues and is boldly articulated, 

 the free portion immediately beyond the skin being curved backward and more closely 

 articulated or striated transversely, the striae becoming even more closely arranged as the 

 organ dilates distally, viz. about the termination of the opaque striated central region. 

 The rest of the tip is pale, translucent, and curves slightly forward to the point. These 

 hooks of the fourth segment have shafts (transversely striated) and longer flattened tips 

 than those behind. Moreover, the elongated tip in some is scarcely bent. It is clear 

 that this is only a modification of an articulated bristle, and leads the way to the typical 

 hook (Plate CIV, figs. 1 c and 1 d), which has a shorter and more distinctly curved golden 

 tip, the very fine transverse striations passing considerably beyond the opaque central 

 obliquely striated region. The greater part of the shaft of the hook (more than two- 

 thirds) is inserted in the tissues, so that the leverage is great, and the concavity of the 

 hook is generally directed forward. Each segment has as a rule three or four of these 

 hooks in transverse series at nearly equal distances, and they are latero- ventral in position, 

 probably in connection with the habits of the species in its tunnel. In very large 

 examples from Bressay Sound the first four feet had four hooks protruding externally, 



