310 SYNOPTIC COLLECTION. 



there are also regular rows of papillae encircling the body 

 (figs. 3, 4). 



It is interesting to note that the larva of another 

 Gephyrean, Phascolosoma vulgare Dies. (No. 769, model), 

 possesses setae which are lost before the animal attains 

 adult size. This is probably owing to the habit of the 

 worm of living in a shell, usually a univalve, that it has 

 found on the beach. The opening being too large, the 

 animal builds out a long tube composed of mud and sand 

 cemented together by a secretion of its body. The large 

 plump body stays within the shell, while the long pro- 

 boscis is put out of the tube. 



The development of Sipunculus is remarkably abbre- 

 viated (Hatschek). Even the larva shows no trace of 

 segments, such as we have seen in the larva of Echiurus. 



This genus differs from the majority of worms by hav- 

 ing distinct longitudinal ridges extending from one end of 

 the body to the other. The shape of the body is 

 peculiar. The extreme forward end from which the pro- 

 boscis extends (No. 770, Sipunculus tessellatus} is small as 

 compared with the rest of the anterior region, which is 

 greatly swollen. Near the middle, the body decreases in 

 size only to swell out at the posterior end. The mouth 

 is surrounded by tentacles, and the anus is situated on 

 the dorsal side of the anterior region. 



The preparation (No. 771) shows the long alimentary 

 canal which in the animal coils and bends upon itself and 

 ends in the anterior region as already stated. The four 

 large retractor muscles of the oral sac and their points of 

 attachment to the wall of the body are also clearly seen. 



Besides these muscles, Sipunculus is unusually well 

 supplied with locomotor muscles, having three sets, cir- 

 cular, oblique, and longitudinal. 



The nerve cord is visible in the preparation (No. 771) 

 as a white thread extending from one end of the body to 

 the other. 



One species of this genus, S. nudus (No. 772) is pro- 



