6 10 THE ANIMAL KINGDOM. 



small prostomium, a large peristomium, a segmented body, which terminates in two 

 processes armed with adhesive papillae. The two prostomial tentacles contain each 

 a tube with muscular walls, which terminates in the peristome in a saccule. The 

 two tubes are connected by a cross branch. Each somite is provided with a pair 

 of latero-dorsal bundles of setae contained in a sheath, capable of protrusion and 

 retraction. Oblique dorso-ventral muscles are well developed, and cut off two 

 lateral coelomic chambers from a median chamber. Transverse septa are present. 

 The nervous system is wholly contained in the hypodermis. It consists of a supra- 

 oesophageal ganglion, oesophageal commissures, and two ventral cords, the latter 

 being connected by a single transverse commissure in the peristome. Ganglionic 

 (hypodermic) cells cover the supra-oesophageal ganglion above and below, the 

 ventral cords only on their external surface. Two pigmented eye-spots are con- 

 tained in the supra-oesophageal ganglia, and there is a pair of large ciliated cephalic 

 grooves. The mouth is ventral, the anus dorsal and terminal. The digestive tract 

 consists of an oesophagus with an intestine constricted where it traverses the septa. 

 Both are ciliated throughout. A dorsal vessel has been observed. A pair of 

 nephridia are present in each somite, and traverse the septa, as in all Oligochaeta. 

 Their external apertures are near the setigerous tubes. The sexes are separate. 

 The testes and ovaries are small cellular masses affixed to the posterior faces of the 

 septa in the intestinal region. Their cells are detached and ripen in the coelome. 

 The sexual products are conveyed outwards by the nephridia. The nephridial 

 apertures in the sexual somites of the male are papilliform, and probably copulatory. 

 The sexual somites of the female contain a pair of vesicles, which are filled with 

 spermatozoa ; their ciliated ducts open latero-ventrally. 



Marion and Bobretzky, Anne"lides du Golfe de Naples, A. Sc. N. (6), ii. 1875, 

 p. 69. Nervous system, Fraipont, Archives de Biol. v. 1884. Larva, see Claparede 

 and Metschnikoff, Z. W. Z. xix. 1869, p. 175 ('an undetermined Spionid larva'). 

 Development, Repiachoff, Z. A. iv. 1881. 



The classification of the Chaetopoda is as follows 



I. Polychaeta : marine, with the setae implanted in parapodia, there being 

 many setae in a bundle ; antennae and palpi usually present on the prostomium ; 

 cirri and branchiae on the somites of the body. The sexes, as a rule, separate ; 

 development accompanied by a metamorphosis. 



(a) Errantia : free and carnivorous. Prostomium large and more or less 

 independent ; usually furnished with eyes and well-developed antennae ; body 

 seldom divided into regions; parapodia large; pharynx generally protrusible. 

 Aphroditidae, Euniddae, Nereidae, Syllidae, &c. 



(b} Tubicola s. Sedentaria : vegetable feeders ; tubicolous ; the tube some- 

 times fixed. Prostomium small ; body frequently divided into regions ; parapodia 

 small; pharynx short, sometimes eversible, but never armed with teeth. Capitel- 

 lidae, Arenicolidae (= Telethusidae], Chaetopteridae, Chlorhaemidae, Terebellidae, 

 Serpulidae, &c. 



II. Oligochaeta. No antennae, parapodia, cirri, or branchiae; setae some- 

 times absent; hermaphrodite; sexual organs restricted to a limited number of 

 somites ; special sexual ducts present ; ova laid in a cocoon ; no metamorphosis in 



