412 DR J. H. ASHWORTH 



beyond -the lips of the chaetal sac. There are generally four to six fully formed 

 chaetae of this type, and two to five in course of formation, constituting the most 

 anterior row of chaetae in the notopodium. 



(ii) Stronger chaetae (the "acicula" of Saint-Joseph), which lie in a row close 

 behind the chaetae just described. These chaetae (text-fig. 3, B), which are about 

 "5— *55 mm. long and attain a diameter of 24-28^, are curved distally, and project con- 

 siderably beyond the lips of the chsetal sac (PL XXXVII, fig. 8). Each chaeta usually 

 presents a blunt tip, but if one of these chsetae be examined before it has come into 

 use it is found to be pointed at the tip and to be there enveloped by a flat sheath 

 (visible as a delicate lamina on each side of the chaeta), which also runs out into a fine, 

 flexible tip (text-fig. 3, B'). When the chseta comes into use, the tip of the sheath is 

 worn away ; then the laminae break up into minute pointed processes and soon 

 disappear, and the tip of the chaeta itself becomes blunted, assuming the form shown 

 in text-fig. 3, B. There are usually three to five of these chaetae in use, and two or 

 three in course of formation. 



(iii) Capillary chaetae, the maximum diameter of which does not exceed 4// 

 (text-fig. 3, C). These taper gradually to fine points. From eight to fifteen fully 

 formed chaetae of this type, each about *5-'55 mm. long, are present, together with a 

 few in course of formation. In one specimen the first notopodium of each side bears, 

 among the capillary chaetae just described, one or two slightly stouter and shorter 

 bristles (text-fig. 3, D) which taper more rapidly at their free ends. These chaetae 

 are about '3 mm. long and 5/* in diameter. 



The series of stronger chaetae (text-fig. 3, A, B) arise in two closely apposed rows 

 near the bottom of the large chaetal sac, while the slender chaetae (C, D) arise more 

 dorsally and on the posterior wall of the chaetal sac. The two series of stouter 

 chaetae stand well in front of the slender ones. The latter usually point backwards, 

 while the strong, curved chaetae (the straight chaetae (A) in the anterior row are 

 usually scarcely seen on external examination of the specimen) point in a quite 

 different direction, either antero-dorsally or latero-dorsally. As the stout and slender 

 chaetae are so different in appearance and direction, and are comparatively widely 

 separated from each other at their exits from the chaetal sac, it is scarcely surprising 

 that the curved chaetae have not been considered to be part of the notopodial 

 armature, but have been referred to a region between notopodium and neuropodium, 

 the notopodium being regarded as having capillary chaetae only. There can, how- 

 ever, be no doubt that the strong chaetae belong to the notopodium. The lip of the 

 chaetal sac immediately to the outer side of the curved chaetae is very well developed, 

 forming a prominent feature of the first chaetiferous segment (fig. 8). 



The first neuropodium is a simple conical elevation bearing capillary chaetae 

 only. These appear to be arranged in two rows — an anterior row of about eight or ten 

 chaetae similar to that shown in text-fig. 3, D, and a posterior row of thirty or forty 

 longer ami more slender chaetae like that represented in text-fig. 3, C. 



