250 J. H. ASHWORTH. 



The setas of S. inf latum are lodged in sacs in the para- 

 podia^ and the tips of the bristles project bej^ond the promi- 

 nent lips of these setal sacs. On first examining a para- 

 podium only the simple capillary setse are seen, but after 

 rendering the tissues more transparent by treatment with 

 warm potash solution the furcate setas become visible. The 

 simple setae project a long way beyond the mouths of the 

 setal sacs, being exposed for quite half their length, while 

 the furcate setae are almost entirely enclosed, only their fine 

 tips protruding from the mouths of the sacs (fig. 9). 



The setse of a parapodium maybe divided into four groups, 

 there being one group or row of simple setae and one of 

 foi'ked setae in each notopodium and neuropodium. The 

 simple setae of the notopodium and neuropodium form two 

 straight fascicles, projecting from the parapodium in almost 

 parallel or in very slightly diverging lines; but the furcate 

 setas lie in two bundles, which are usually placed so that while 

 their proximal ends are adjacent their tips are widely diver- 

 gent, those of the notopodium being directed dorso-laterally, 

 and those of the neuropodium veutro-laterally. The bundles 

 of furcate and simple setae form two almost vertical and 

 parallel rows in each ramus of the parapodium. The row of 

 forked setae is usually the inore anterior. 



The simple setae are fine capillary structures, attaining a 

 length of about 1*7 mm. in the largest specimen (56 mm. 

 long). They are about 8 ^ in diameter at their inner ends, 

 where they are thickest, and taper gradually to a very fine 

 point. They are marked in their proximal portion by very 

 minute longitudinal ridges and furrows. Those setas which 

 have not been worn by use bear exceedingly minute hair-like 

 processes on their distal third (fig. 26). 



The length of the furcate setae is generally about three 

 fourths that of the simple setse of the same parapodium. In 

 the specimen, 56 mm. long, they reach a length of 1*2 — 1'3 

 mm. They are considerably stouter than the simple setae, 

 being 15 — 18 fx in thickness at their inner ends. They taper 

 gradually to the base of the fork, their diameter at this point 



