The Central Nervous System of a 

 Sipunculid 



WILLIAM A. HILTON 



A number of specimens of the genus Phascolosoma were ohtaineti 

 at Laguna Beach. These were preser\ed in \arious fluids. Plem- 

 ming's fluid and mercuric chloride, were especially valuable for 

 study. The ner\e cords were dissected out and mounted after stain- 

 ing. Some were imbedded, sectioned and stained. The stain which 

 brought out the cells with greatest clearness was copper haema- 

 toxylln. 



The general character of the ner\-ous system of sipunculids Is well 

 known, and the specimens examined at this time were typical as to 

 the form of the brain and cord. The brain Is imbedded in the pro- 

 boscis iust below the tentacles. It has a similar appearance In 

 section to the photographs of Spengel, 1912. The brain is small. 

 Two main branches supply nearby tentacles and muscles. There 

 is a pair of small branches from the connecti\es. Extending from 

 the epithelium of the tentacular region is a pair of tubes leading 

 into the brain, the cerebral organs. These epithelial tubes lead 

 to a pigmented area on each side, and these pigmented areas in 

 section look like simple eyes. A few irregular spots of pigment 

 were found near the larger masses. The epithelium at the outer 

 end of the tube was also deeply pigmented. 



Throughout the body the \entral nerve cord kept about the same 

 width, although the muscle bands at the sides Increased somewhat. 

 The strands connecting the muscles and ner\es to the animal's body 

 were more or less regularly arranged. In specimens with the pro- 

 boscis drawn In, the ner\e cord Is of course doubled back on itself. 

 In the specimen drawn at the junction of the two parts, that of the 

 proboscis and that of the ventral body-wall, there is a lack of lateral 

 branches, as shown in the upper portion of the second line of the 

 drawing. Towards the caudal end the lateral branches come oft 

 more Irregularly. 



When the animal is contracted the neiAC cord seems to be seg- 

 mented, but sections show that this appearance Is ihie to the slight 



