Introduction to Animal Morphology. 223 



coiled ; stomach with a spiral appendage. Siphonostomum 

 gelatinosum has two ciliated head-lobes. 2. Hermellidce 

 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 palece on the prostomial 

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

 cemented shells. 3. Terebellidse inhabiting soft, fragile 

 tubes ; heteronomous with two regions ; head with neither 

 palece 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 (Scalis), or elongated ; anal 

 cirri one (Scalis), or two (Amphicteis). 5. Sabcllida; 

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

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

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

 temporary (Amphicorina, Fabricia) open at both ends, 

 rosabella has no sheath for the body. Myxicola has two 

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

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

 'd, witli no parapodia; blood with red corpuscles; its 

 larva is the form called Actinotrocha. The tube in Sabclla 

 en only at one end, and membranous. Protula has a 

 nil dermal expansion. P. Dystcri is hermaphrodite. 

 tubicolous, heteronomous, with two ciliated 

 skin i the front segments ; the ^ills have a spiral basis, 



with one or two ojercula with chitinous or calcareous discs; 

 . or Hue ; the lubes are attached to slo: 

 . worm-like (Serpula), spirally rolled (Spi- 

 rorbis), or free (Ditrupa). Filo-ra:, I the base of 



the gills. 



