300 DR J. H. ASH WORTH 



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

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

 anterior row of choatse in the notopodium. 



(ii) Stronger chsetse (the "acicula" of SAINT-JOSEPH), which lie in a row close 

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

 '5-'55 mm. long and attain a diameter of 24-28^, are curved distally, and project 

 considerably beyond the lips of the chsetal sac (Plate, fig. 8). Each chseta usually 

 presents a blunt tip, but if one of these chsetse 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 chseta), which also runs out into a fine, 

 flexible tip (text-fig. 3, B'). When the chseta conies 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 chseta itself becomes blunted, assuming the form shown 

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

 three in course of formation. 



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

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

 formed chaetse 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 chsetEe just described, one or two slightly stouter and shorter 

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

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



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

 near the bottom of the large chsetal sac, while the slender chsetse (C, D) arise more 

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

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

 while the strong, curved chsetse (the straight chtetse (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 

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

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

 that the curved chsette 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 clisetae only. There can, how- 

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

 rli;i't;il sue immediately to the outer side of the curved chsetse is very well developed, 

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



The first aeuropodium is a simple conical elevation bearing capillary chsetse 

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

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

 longer and more, slender c.liaetse like that represented in text-fig. .', (J. 



(ROY. SOC. KIIIN. TRANS., VOL. L, 412.) 



