Gatty Marine Laboratory, St. Andrews. 175 



The succeeding region of the body is characterized by the 

 increase in the depth of the lateral lamellae, the first being 

 about three times that of the next in front; but they 

 gradually diminish in depth in their progress backward, 

 whilst they increase in prominence, those in the distal part 

 of the region, for no dorsal bristles are visible, projecting like 

 cirri. The bristles of the region are thus pushed ventrally, 

 so that even the long posterior forms are not, as a rule, seen 

 at the sides in a dorso- ventral view. They are situated to 

 the inner side of the prominent, coloured, lamellae forming 

 the dorsal region of each segment. The longest bristles in 

 each tuft are in front, since, instead of being arranged in a 

 transverse row, they form an oblique one. The typical 

 bristles are long and translucent with smooth shafts, which 

 taper from the skin to the delicate and flexible tip covered 

 with whorls of spikes directed distally. Their usual direction 

 is forward and inward, and they fall smoothly under a needle, 

 carried from behind forward, but rise against it when passed in 

 the opposite direction. As rudimentary bristles of the same 

 kind appear in the first region of the body between the bases 

 of the spathulate forms, their distribution is thus uniform 

 throughout. Moreover, the bristles of the first series of this 

 region present a trausition-stage, having stouter shafts and a 

 broader and shorter spinous part at the tip, the latter, indeed, 

 resembling a short villous region. Accompanying these is 

 usually a slender tapering spinous bristle, and this is also a 

 transition-form. The posterior bristles form a conspicuous 

 series ventrally, but, though longer, their structure remains 

 the same. 



The prominent transverse or lateral lamelhe formerly 

 alluded to bear the numerous hooks, their tendons, and 

 muscles. Tn shape the hooks are elongate, with a single 

 tendon at the distal end and two at the rounded base. In 

 lateral view five teeth usually characterize theni, though 

 when viewed from the front each represents only one of two 

 or three in the row of which six may occur in both anterior 

 and posterior feet, the latter, however, having smaller hooks. 

 The slender cirriform lamellae of the posterior feet have the 

 interior largely occupied by the bundles of tendons from the 

 hooks, and to these muscular fibres are attached. At the 

 base of each elongated lamella posteriorly is a deep brownish 

 pigment-spot. 



The narrow posterior end of the body is continued as a 

 long tubular process, which fits into the dorsal groove when 

 the animal is quiescent in the tube, but which can be 

 elongated or shortened at will, and forms a very efficient 



