356 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 97 
but beginning at O' the lining is coarsely plicated longitudinally, 
and these rapidly become more strengly marked (unless wall is 
infiated). ‘Toward the end of the descending spiral they gradually 
fade out. 
The thick collapsed nephridia, about 40 mm. long, have the walls 
fortified by an irregular net of stout muscle bands. The intervals 
are inflated into shallow pockets of various sizes, having the appear- 
ance externally of miniature cauliflowers. The nephrostome, on the 
anterior side of base, is between muscles 11-12 (left) and 12-13 
(right). In the paratype this is reversed. There is not a marked 
anterior lobe of nephridium projecting forward over the nephro- 
stome as in nudus. 
imm. 
Ficure 54.—Larva of Sipunculus polymyotus, new species, from left side, X 20: The retractor 
muscles attached to body wall and head region are of the left side only. Muscle bands 
of body wall omitted. (4, anus; G, glands; J, introvert, with nerves from nerve cord 
NC; NL, left nephridium; RD, dorsal retractor, RV, ventral retractor; S, stomach- 
intestine; the muscle strand apparently attached to it is fastened to the body wall.) 
The dorsal vessel is either finely papillated or smooth and extends 
backward as far as the posterior edge of the mesenteries that anchor 
the esophagus to the ventral retractors. The ventral vessel is small- 
er, 1s not quite so long, and contains light-yellow material. 
Anteriorly the nerve cord is held between two strong ventral 
paraneural muscles. On the anterior border of the brain is an aston- 
ishingly large, pale yellowish cerebral organ (frons), the subdivisions 
either very slender or flattened, thin, and digitate (pl. 10, fig. 2). 
The longest are 3.6 mm. In S. nudus the frons is a transverse pad. 
Color of specimens preserved in formalin, medder brown; alcoholic 
specimen, faded buff (‘‘museum color’’). 
