CHAETOPODA. 597 



into three longitudinal chambers, a median containing the digestive tract, 

 and two latero-inferior 1 . It is also divided by transverse fibre-muscular 

 septa into a series of more or less complete chambers, one behind the 

 other. The septa are well-developed in Oligochaeta (except Aeolosoma\ 

 Errantia, and many Tubicola^ whilst in other Tubicola only one or two 

 may be present in the anterior region of the body. The chambers thus 

 made communicate either round the intestine, round the ventral vessel, 

 or by pores variously placed. They are provided with dorsal pores opening 

 outwards in many Oligochaeta 2 '. The muscular tissue is composed of cells 

 with a superficial fibrillar striated layer, and usually but a slight remnant 

 of protoplasm surrounding the nucleus. A nucleated connective tissue 

 intervenes between the muscle-cells. It is largely developed in the 

 anterior region of the body in many Serpulidae and reduces the coelome 

 to two narrow passages. The coelomic surface of the body-walls as well 

 as of all the internal organs appears to be covered by an epithelium, which 

 varies in character not only in different regions of the body but in different 

 Chaetopods 3 . This coelomic epithelium is ciliated in the Aphroditidae, 

 polycirrine Terebellidae, and the Anangian Glyceridae. 



The nervous system consists of a pair of cerebral or supra-oesophageal 

 ganglia and a ventral nerve cord, the oesophageal commissures connecting 

 them and a variously developed stomato-gastric system in connection with 

 the pharynx. The dorsal surface of the cerebral ganglia, the ventral 

 surfaces of the ventral ganglia are in contact with the hypodermis in many 

 Polychaeta. The posterior termination of the nerve-cord in Telepsavus 

 costarttm, the whole nervous system of a Terebella sp. ?, from Heligoland 

 (Semper), and of Aeolosoma (which is reduced to the cerebral ganglia), are 

 included in it as in certain remarkable and primitive worms 4 . The cerebral 

 ganglia are simple in Oligochaeta^ complex in many Polychaeta in which 

 they consist of antennary and stomato-gastric centres, the former supplying 

 the antennae, the latter the palpi or their branchial homologues in some 

 Tubicola (cf. note, p. 593). The first two or three ventral ganglia may be 

 united 5 , the remainder are usually distinct. The ventral cord of some 

 Tubicola (Polydora, Serpulidae) is ladder-like, the right and left half of 



1 Bands of muscles are stated to pass across the coelome beneath the intestine, and from one 

 parapodium to another in Glyceridae. 



2 See on these pores p. 199, ante. Add to what is there stated that the position of the first pore 

 appears to constitute a specific character, and that in one instance at least the worm possesses, when 

 irritated, the power of expelling through them a jet of coelomic fluid to the height of two feet. See 

 Vorderman, Tijdschr. fur Nederl. Indie (8), ii. 1882 (Naples Zool. Jahresbericht, 1882, ' Vermes,' 

 p. 273). Our English Earthworm suffers coelomic fluid to escape sometimes if pressed by the 

 fingers. 



3 See on Arenicola and Lumbricus, Viallanes, A. Sc. N. (6), xx. 1886. 

 * I.e. the Archi-Chaetopoda, p. 609, and Archi- Annelida, p. 613. 



5 In Ophelia ( Tubicola) a ganglion is situated on each oesophageal commissure, and supplies the 

 first pair of feet (Pruvot). 



