86 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.15 



nephthys Friedrich. Since the lateral margins of these cirri are some- 

 times heavily ciliated, they have been thought to be branchial in func- 

 tion. 



The ciliary mechanism of the interramal cirri has been studied in 

 some detail (Coonfield, 1931 and 1934) based on Nephtys bucera 

 Ehlers. Here the cilia on the parapodia are in a single row, beginning 

 on the outside of the interramal cirrus at its base, continuing around 

 the tip on its inner side and extending on the body wall to the base of 

 the neuropodium. In these regions the cilia are grouped into small tufts. 

 Each tuft is limited to a single cell and consists of 40 to 50 large com- 

 pound cilia; each compound cilium is again made up of smaller units. 

 Physiological tests performed by Coonfield (loc. cit.) indicate that 

 each ciliated cell is independent of the nervous system, regulating its 

 own activity. The coordination attained in situ is believed to be depend- 

 ent on a neuroid mechanism. The effective beat of the cilia is from the 

 head of the worm toward the tail. This beating causes a current of 

 water to flow on each side of the worm posteriorly in the groove formed 

 by the division of each parapodium into a neuropodium and a noto- 

 podium. 



The neuropodium resembles the notopodium in its setal parts but in 

 reverse order; at its lower base is a tapering ventral cirrus. In some 

 species the superior edge has an erect process or accessory neuropodial 

 lobe (pi. 18, fig. 3) (=accessory branchia of some authors). The body 

 tapers backward and ends in a narrow, collarlike pygidium with a long 

 median, filiform process or also a pair of shorter ones. 



All setae are simple, not articulated, and they may be of several 

 kinds. They are arranged in preacicular and postacicular, fanshaped 

 fascicles. According to kind they occupy certain positions. Those in 

 preacicular position are transversely barred (pi. 13, fig. 9) in their 

 distal free portion and taper to slender pointed tips. The alternating 

 light and dark areas of these setae (sometimes called fenestrated) are 

 due, not to external ridges, but to an internal structure of alternating 

 harder and softer substance. Postacicular setae are usually longer (except 

 in some anterior segments where they may be weakly developed) coarser, 

 and often bladelike. They are sometimes called lanceolate setae. They 

 may be quite smooth, especially those at the ends of the series, or the 

 outer cutting edge may be serrated (pi. 13, fig. 4) or denticulate (pi. 

 15, fig. 4) or diffusely spinose (pi. 18, fig. 5) or with a few large teeth 

 near the base (Nephtys picta Ehlers), or there may be a large spur near 

 the base (pi. 16, fig. 5). This character has been found to be highly 

 specific in the species investigated ; it also shows a remarkable degree of 

 specialization. 



