SABELLIDAE. 467 



abdomen in which the relations of the setae arc inverted, the capillary forms 

 being ventral and the uncini dorsal. Rarely there are no crochets on the thoracic 

 somites (Caobangeinae). 



The prostomium proper is not distinct, being hidden by the peristomium, 

 which is carried forward and usually shows a distinct collar. The prostomium 

 bears two large lobes, commonly regarded as the greatly developed palpi, right 

 and left respectively, which carry branchiae on which are barbules arranged in 

 two series, the branchiae inserted in a circular arc, or in several turns of a spiral. 

 The tentacles are very small, often showing only as slight, sensory tubercles. 

 Eyes, often composite, may be present on the branchiae. No cirri are present. 

 Hence, no thoracic membrane. 



The capillary setae have various forms of much service in classification. 

 The uncini are in form either avicular or pectinat'e, or in some cases with long 

 manubria. 



A median ciliated groove extending forward from the anus to the anterior 

 end carries faecal matter out of the tube. Usually ventral in position, it often 

 curves dorsad on the thorax. 



There is no protrusible proboscis and no pharynx. 



Ventral gland shields present on abdomen as well as on thorax. 



The tube is formed of more or less transparent mucin of variable consistence, 

 usually strengthened by mud, grains of sand, fragments of shells, or other adher- 

 ent materials. The mud strengthening the tubes often has a tough consistence 

 almost like that of caoutchouc. Some show a marked colonial tendency, the 

 lower parts of their tubes, which lack the supporting wall of mud, being united 

 together and attached to a common support. The tubes of the boring forms 

 remain membranous. 



The size of sabellids varies from a few miUimeters only, on the one hand, to 

 five hundred millimeters or more on the other, the number of somites varying 

 correspondingly from near twenty to more than six hundred. These forms 

 are often of different and brilliant colors, the expanded branchiae in particular 

 showing a varied brilliance and beauty. 



The sabellids nearly always remain within their tubes, though it has been 

 shown that they may exceptionally leave them and swim about freely, as St. 

 Joseph has demonstrated in the case of Bispira elegans (St. Joseph) and Myxicola 

 dinardensis St. Joseph (Ann. sci. nat., 1894, ser. 5, 17, p. 316, 324), and Gravier in 

 that of a young Laonome elegans Gravier (Nouv. arch. Mus. hist, nat., 1908, ser. 

 4, 10, 1908, p. 101). While living ordinarily in more or less shallow water, some 



