Gatty Marine Laboratory ^ St. Andrews. 23 



shafts, wliich taper a little as they approach the tip, which 

 is fiiit'iy tapered, distinctly curved, serrated, and furnished 

 with narrow wings — these, indeed, in some being indistinct. 

 These bristles, moreover, sliow a gradation posteriorly, where 

 shorter forms with nearly straight ti|)s and somewhat wider 

 wings occur. The second series forms a dense brush con- 

 siderably shorter than the foregoing, and, as in other forms, 

 the two groups are moved by separate muscles, so that 

 their special functions may be performed. The shafts of 

 the longer bristles of this group are similar to those of the 

 tirst series, but shorter and slightly stouter, and the shorter 

 tapered tips have a trace of a curve, and have wider wings, 

 but soou a tendency to form a tip like a knife-blade, in 

 which the wings are fused, is apparent, and by-and-by all 

 the shorter bristles have the translucent flattened tip. 

 This blade varies in length and breadth, as well as in 

 curvature, but the majority of the bristles in these tufts are 

 of this formation. The peculiar flattening of the tips, 

 which are thinnest distally, gives great flexibility to the 

 organs, so that their function of smoothing and brushing is 

 facilitated. All have strong, striated, golden shafts, which 

 gradually dilate from their translucent bases to the distal 

 third, when gentle narrowing again occurs to the origin of 

 the flattened tip. When softened and compressed in gly- 

 cerine, the various stages in the transformation of a winged 

 form, with an elongated tapering tip and with bold striie on 

 the wings, to a form iu which the tip is broad, flattened, 

 and translucent with but a trace of minute striation, can be 

 followed. With the change of feet in the second division of 

 the body, a reversion to the normal ty|)e of bristle takes 

 place, the fascicles consisting of smaller shorter bristles of 

 nearly equal size, with finely-striated straight shafts, similar 

 in formation to the preceding, but which have narrow wings 

 gradually disa^jpearing on the delicately-tapered tips, the 

 minute serrations on the edges being continued far up- 

 ward. These bristles are grouped in a tulip-like tuft, and 

 each resembles the blade of a pointed scalpel, only a trace 

 of a wing appearing toward the convex edge, which is 

 serrated, the lines sloping outward and upward. De St. 

 Joseph counted sixty long bristles and two hundred shorter 

 in the sixth segment of an example 13 cm. long. In the 

 posterior region the bristles form a cylindrical pencil, a 

 slight swelling occurring distally where the wings project. 

 Their tips are more finely tapered than in the first region, 

 and there is a slight curvature at the connnenccment of 

 the wings. The pencil springs from a distinct setigerous 



