﻿SIPUNCULID WORMS OF CALIFORNIA — FISHER 379 



introvert and the four retractors occupy about one-seventh of the 

 body length. The retractors are free from one another and arise at 

 approximately the same level. Both vcntrals arise from muscles 1-4, 

 while both dorsals arise obliquely from muscles 7-11. The two 

 protractors arise from muscles 12-15 at the posterior border of the 

 introvert. Before insertion, 4 mm. in front of the brain, they pass 

 over the dorsal retractors. Their form and position, with the introvert 

 out and in, are shown in plate 19, figures 1 and 2. The rectum passes 

 far forward and opens close behind the (dorsal) origin of the pro- 

 tractors. (Muscles 17 and 18 are the two middorsal in figure 1; 18 

 and 19 are really 17 and 16 of the left side.) The rectum lacks thin, 

 fan-shaped wing muscles. A slender spindle muscle arises from the 

 ventral wall of rectum, 20-24 mm. behind anus; two roots proceed 

 toward anus in the wall of the rectum, while the free muscle proceeds 

 backward following the gut; 10-12 mm. from its origin is a very 

 small coecum to which it is attached. The rectum is fastened dorsally 

 to the body wall by a continuous mesentery, as far hack as the two 

 lateral anchors just behind the origin of the spindle muscle. These 

 short lateral strands of tissue fan out slightly and may be rudiments 

 of the rectal wing muscle. At any rate, to them are attached the 

 ends of a delicate filament, forming a loop, which on each side passes 

 obliquely ventral ward along the origin of the dorsal retractors 

 Here the thread is thickly beset with delicate racemose structures 

 (poorly preserved). These quicldy thin out posterior to the muscles 

 and the rather long posterior loop is very delicate, translucent, and 

 more loosely attached to the coelomic epithelium. Probably the 

 "bandformiges Organ" figured by Selenka (1883, p. 109, pi. 12, fig. 

 174, y) in S. mundanus is a fragment of a similar structure. It re- 

 sembles a gonad, but may be a more extensive "Zottenbildung." 



The alimentary canal is macerated, but it appears to lack the for- 

 ward loop that complicates the anterior end of the spiral of typical 

 Sipunuculus. Although in plate 19, figure 1, the esophagus is drawn 

 to the right, it naturally turns to the left, for its first attachment to 

 the dorsal wall is by separate fixing muscles, along muscle band 9 

 (or 8) of the left side. The mesentery between the esophagus and the 

 left dorsal retractor extends posteriorly only about half as far as the 

 right. This shorter left mesentery allows the ventral vessel to become 

 sinistral, while the dorsal vessel gradually becomes dextral. Both 

 end dorsolaterally at the beginning of the dorsal fixmg muscles. From 

 here the alimentary canal passes backward along muscle 9, for an 

 unkno^Aii distance, before starting the spiral. The spirals are well 

 established in the posterior half of the body. 



Nephridia are long, slender, and except for a short terminal portion 

 are closely attached to muscle 5. 



