392 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



appearance. When retracted these organs appear externally as elongate 

 slits (pi. 47, fig. 4) ; when everted they are sacklike, ciliated mounds. 



The proboscis is a soft, eversible part of the anterior end of the ali- 

 mentary tract. When everted it is globular to somewhat lobed (pi. 50, 

 fig. 1 ) ; its surface may be smooth to more or less strongly papillated, 

 especially in its proximal part; the separation between the 2 regions is 

 sometimes abrupt. The proboscis functions in locomotion and for food 

 ingestion. 



The thorax consists of a definite number of segments, ranging from 



only 9 {Capitella, see below) to as many as 19 or 20 {Anotoiiiastus, new 



genus, see below). The first visible segment or peristomium may be 



achaetous and apodous (Notomastus) or it may resemble those farther 



back (Capitella). The first setigerous segment may be complete with 



both notopodia and neuropodia (Heteromastus) or neuropodia may be 



absent {Leiocapitella, new genus) ; all other parapodia are biramous. 



Thoracic parapodia are provided with only simple pointed setae 



(Noto7nastus), or also hooded hooks (Heteromastus), or also specialized 



genital hooks (Capitella). Abdominal parapodia are provided with only 



simple hooded hooks (Notomastus), or also slender pointed setae (Proto- 



capitella), or also specialized spines (Scyphoproctus and Pulliella). 



Branchiae are absent (Capitella), or present on the abdomen as non- 



eversible modifications of notopodia or neuropodia (some species of 

 Notomastus and Heteromastus), or they may be eversible sacks or lobes 

 from either notopodia {Heteromastus magnus, new species) or neuro- 

 podia {Dasybranchus lumbricoides Grube). 



Lateral sense organs (pi. 50, fig. 1) are seemingly absent (pi. 45, 

 fig. 1) in some (Capitita, new genus), or limited to thoracic and anterior 

 abdominal segments (Heteromastus), or present throughout (Dasy- 

 branchus). On the thorax they are eversible, on the abdomen stationary, 

 papillae. They are usually to be found on, or near, or along the para- 

 podial ridge located between notopodia and neuropodia. Like the nuchal 

 organs, they are ciliated mounds without aperture but provided with 

 neural innervation and muscular connections. They probably function 

 in sensory detection. 



Nephridia, sometimes though perhaps incorrectly called segmental 

 organs (since they do not occur on all segments), open externally by a 

 pore and internally through a nephrostome into the coelomic cavity. 

 Their presence or stage of development in immature through adult stages 

 is usually variable since the constituent parts change during ontogeny. In 



