306 polvchakta 



By their arrangement the body is divided into a thorax oi' nine 

 segments and an abdomen ; in the former the capillary chaetw 

 are dorsal, and in the latter ventral. The buccal region is not 

 eversible ; there is no pharynx. The septa are regularly developed 

 in the abdomen, but are absent in the thorax ; the nephridia are 

 dimorphic; there are two large ones in the thorax opening by a 

 median dorsal pore just above the brain; those of the abdomen 

 are small funnels, and act as genital ducts. The worms are 

 tnbicolons ; " gland-shields " are present on the thoracic segments. 

 Sub-Order 2. Hcrmelliformia. The peristominm (Fig. 135) is 

 enormously developed, and forms a bilobed hood capable of closing 

 over the month ; the truncated free end of each lobe carries three 

 semicircles of peculiar chaetae, which act as an efficient protec- 

 tion when the worm is withdrawn into its tube. The prostoinium 

 is very small, but retains a pair of well-developed tentacles ; the 

 palps, which are subdivided as in the Sabelliformia, have become 

 fused with the ventral edges of the peristomium, and appear as a 

 series of ridges on each side, carrying numerous filaments. The 

 thorax consists of five segments, the notopodia of three of which 

 are well developed and bear strong chaetae ; dorsal cirri are 

 present along the greater part of the body, and act as gills. The 

 arrangement of the chaetae and of the internal organs is as in the 

 Sabelliformia. The worms form tubes of sand. 



BEANCH A. PHANEEOCEPHALA. , 



Sub-Order 1. Nereidiformia. 1 



Fam. 1. Syllidae. These are small worms, the majority being 

 less than an inch long, so that they are not easily observed. 



1 The character of head and parapodium in each family will be gathered from the 

 figures accompanying the general description in Chap. X., so that detailed descrip- 

 tion is unnecessary. In all cases the chaetae form valuable specific characters. 



The examples of the various families are British, unless the opposite is expressly 

 stated ; but most of them are not confined to our shores, and the foreign locali- 

 ties are usually given. No attempt is made to enumerate all the British species. 



The following books may be found useful for identifying the worms : 

 Claparede, Recherches anat. sur les Annttidcs observes dans les Hebrides, 1861 ; 



Anndlides CMtopodes du golfe de Naples, 1868, and Suppl., 1870. 

 Cunningham and Ramage, " Polychaeta Sedentaria of the Firth of Forth," Trans. 

 Hoy. Soc. Edinburgh, xxxiii. 1888, p. 635. 



