178 



COE 



on the flats laid bare by the lowest tides in San Pedro Harbor. It has 

 previously been recorded only from the vicinity of Woods Hole, Mass. 

 The worms are found in sandy, and not in muddy locations. 



The species may be recognized by the following characters : Body 

 rather slender, usually 5-8 cm. in length, rather translucent. Head 

 slender, when extended tapering to a fine point, without cephalic fur- 

 rows ; pure white in color. Esophageal region rounded; white, very 



LUi* 



FIG. 22. Z. littoralis. Diagram of anterior por- 

 tion of body, showing relation of cerebral sense organ 

 (cso) to ciliated pit (c/5) on side of head ; rh, rhyncho- 

 daeum ; br t brain ; /, lateral nerve. 



FIG. 23. Z. littoralis. Diagram of caudal cirrus 

 and posterior end of body ; In, lateral nerve, extend- 

 ing into caudal cirrus (In'} ; /, intestine; a, anus. 

 Both figures after C. B. Thompson. 



FIG. 23. 



pale yellowish or flesh color. Intestinal region flattened in life, but 

 rounded after preservation ; color varies from rose to pale yellow, light 

 brown or chocolate brown, being largely dependent on the amount and 

 character of the contents of alimentary canal. Posterior extremity pro- 

 vided with a conspicuous, although slender, caudal cirrus, white in 

 color (text fig. 23), with large central blood space. 



In internal organization, the presence of an internal circular muscle 

 at the beginning of intestinal region, the division of the anterior por- 

 tion of alimentary canal into esophagus proper and stomach, the open- 

 ing of the ciliated canals leading from cerebral sense organs into shallow 

 lateral pits (text fig. 22, cp) in place of cephalic furrows, the absence 



