18 SABELLARIA SPINULOSA. 



bristles are on the ventral side of the cirrus. He also met with a specimen having a 

 double cirrus on the second segment, the bristles emerging between them. Another 

 example had two sets of collar-bristles on the right, whilst the left was devoid of them 

 and the process reduced in size. 



The anterior ("thoracic") region of the body includes three segments with 

 transversely elongated lamellae, each, moreover, having a pair of flattened, ligulate, 

 crenate branchiae which taper to a point and somewhat resemble the horns of a goat or 

 antelope, from their transverse ridges, the large cilia of which have a bold hook-like 

 curve directed toward the tip of the organ. The branchiae are supplied with long, 

 powerful cilia on their ridges, which make a vortex in the water around them, and thus 

 are in marked contrast to the delicately ciliated tentacles. Two vessels occur at their 

 base, apparently afferent and efferent, and between these are a series of parallel 

 transverse branches. They are less sensitive than the pale purple tentacles, since a more 

 violent contraction takes place when the latter are touched with a needle. The first, 

 viz., that in front of the anterior region proper, is a rather broad tongue-shaped process, 

 shorter than the succeeding, which are elongated horn-shaped organs, the sixth 

 apparently being the longest. They continue to the posterior end, but gradually diminish 

 in size. 



Each of the three prominent lateral lamellae below the branchiae carries a series of 

 spatulate golden bristles (Plate CXXIII, fig. 2d) arranged in a single line, the first 

 having seven or eight, the second nine, and the third ten. They are generally directed 

 straight outward, though in life the points are directed backward, and have a flattened 

 translucent tip like the blade of a paddle, the upper end of the shaft gradually dilating 

 into the broad blade, the dilated part, moreover, showing in some short oblique striae 

 on one side — as if a trace of the striae so common in winged forms. Those of the first 

 set have a narrower tip and longer fringes, the outer fringes, moreover, being split into 

 finer processes on the margin. Those of the third series have broader tips and the 

 brush-like filaments at the extremity are shorter. Each bristle diminishes in size from 

 the tip to the base, and the shaft is striated. Mingled with the foregoing bristles are a 

 few simple forms (Plate CXXIII, fig. 2 c), the curved slender tapering tips of which 

 with their sparse spikes project from the skin between the stronger forms. If anything, 

 the first series has slightly narrower tips and more slender shafts than the third, which 

 sometimes shows truncated tips from wear. 



A fold, marked by the purple-brown pigment from each of the dorsal setigerous 

 lamellae, continues the segment ventrally and ends in a papilla with a minute tuft of 

 golden bristles (Plate CXII, fig. 1 b), which, although small, have a similar structure to 

 the larger. They are translucent bristles with long shafts deeply inserted in the tissues, 

 the dilatation of the shaft distaliy being more gradual, whilst the fringes at the tip 

 of the blade pass much more deeply, so that the whole tip forms a more perfect brush. 

 They are also accompanied by the simple spinous bristles, which are considerably shorter, 

 but go more deeply into the tissues. The physiological importance of the two sets of 

 bristles is unknown, but it may be conjectured that the oar-shaped forms, having per- 

 formed their functions of fashioning the tube, could be slightly retracted, or the slender 

 ones may be slightly protracted, so that both might act in a brush-like manner. The 



