Introduction to Animal Morphology. 223 



coiled ; stomach with a spiral appendage. Siphonostomum 

 gelatinosum has two ciliated head-lobes. 2. Hermellidae — 

 tubicolous ; segments heteronomous, of two or three kinds, 

 the hinder thread-like, with no appendages ; the head-lobes 

 are fleshy, cylindrical (Sabellaria), or leaf-like, split (Centro- 

 corone) with a circlet of yellow paleae on the prostomial 

 border, which acts as an operculum. The tube is built of 

 cemented shells. 3. Terebellidae — inhabiting soft, fragile 

 tubes ; heteronomous with two regions ; head with neither 

 paleae nor lobes, but with large, movable, ciliated gills, serving 

 as touch- and prehensile organs ; in most there are 1-3 pair 

 of tree-like gills on the first body-ring, sometimes with a 

 jointed framework. Sabellides has lateral, thread-like gills ; 

 Polycirrhus none. Terebellides has the gills on an azygos 

 medio-dorsal column. 4. Amphicteneidae — tubicolous, hetero- 

 nomous, with three body regions ; prostomium united to the 

 peristome, with a middle lobe and two bundles of thread-like 

 gills ; tail segments with imperfect rings ; gills simply (Pecti- 

 naria) or complexly comb-shaped (Scabs), or elongated ; anal 

 cirri one (Scalis), or two (Amphicteis). 5. Sabellidae — 

 tubicolous, heteronomous, with two body regions ; head-gills 

 pinnate, in two circlets or spirals, one of which may be rudi- 

 mental ; some have eyes on the cirri ; the tube may be 

 temporary (Amphicorina, Fabricia) open at both ends. 

 Heterosabella has no sheath for the body. Myxicola has two 

 head-eyes, four tail-eyes, and forty pair of metameric eyes. 

 Phoronis has the gills on a horseshoe-shaped lobe ; body not 

 ringed, with no parapodia ; blood with red corpuscles ; its 

 larva is the form called Actinotrocha. The tube in Sabella 

 is open only at one end, and membranous. Protula has a 

 ventral dermal expansion. P. Dysteri is hermaphrodite. 

 6. Serpulidse — tubicolous, heteronomous, with two ciliated 

 skin folds on the front segments ; the gills have a spiral basis, 

 with one or two opercula with chitinous or calcareous discs ; 

 blood red, green, or blue ; the tubes are attached to stones, 

 &c., calcareous, worm-like (Serpula), spirally rolled (Spi- 

 rorbis), or free (Ditrupa). Filograna has eyes at the base of 

 the ffills. 



