374 EEPOET— 1891. 



cuticle, in contact with both the sheath and the epidermis. The 

 epidermis is a single layer of squamous cells, and is devoid of mucus- 

 cells, with the exception of those in the heads of the papillas and those 

 scattered in the ciliated region round the mouth, anterior to the first 

 pairs of sette. In this region the papillfe are absent. The setfe of the 

 dorsal and ventral bundles of the fii'st segment are more numerous and 

 longer than those of posterior segments ; they are directed forwards, and 

 form a fan-shaped chevaux-de-frise on each side of the head. Their 

 parapodia form a large continuous fold of the integument, within which 

 the head can be retracted, the setfe then closing in and forming a sort of 

 cage. The posterior parapodia are not well developed ; the dorsal and 

 ventral bundles of seta3 are set on widely separated conical protuberances 

 connected by a slight ridge. The ventral bundles are used for progres- 

 sion, the animal walking on the tips of the setfp, which are inclined 

 forwards and then pulled back in succession from before backwards. 



The alimentary canal, compared with that of other Polychajta (except 

 Pectinaria), is abnormal in being bent on itself several times. The narrow 

 oesophagus opens near the hinder end and on the dorsal surface of a 

 large sac-like, thin-walled stomach, which is continued into an CO-shaped 

 'duodenal' part of the intestine. The stomach, the 'duodenum,' the 

 hinder ends of the pair of uephridia, and the posterior ovaries in the 

 female are enclosed in the septum between segments 9 and 10. This 

 septum forms a complete partition between the ' thoracic ' and abdominal 

 portions of the coelom. It is distended by the viscera named into a large 

 sac, extending as far back as the IGth to 20th segment. It confines the 

 genital products, when they become free, to the anterior part of the 

 body-cavity. It is the only complete septum in the body ; indeed, there 

 is in Siphonostoma no septum anterior to it, but in Troplionia there is 

 also one between the fifth and sixth segments. (I am throughout regard- 

 ing the first setigerous segment as the first behind the head.) The 

 musculature of the body- wall is slight ; there are well-developed retractors 

 of the head. 



The vascular system has attracted attention on account of the dark 

 green colour of the blood in all tlie species of this family. Lankester 

 has shown that the colouring matter, wliich he calls chlorocruorin, is, & 

 body which, like haemoglobin, is easily oxidised and, by suitable reagents, 

 reduced; it also gives a characteristic banded absorption spectrum. 

 Large quantities of blood are contained iu the capacious lacunfe sur- 

 rounding the stomach and intestine. The lacunae have no proper cellular 

 walls, but lie between the basement membrane of the gastric epithelium 

 and a membrane below the peritoneal epithelium. Connected with the 

 enormous lacunas at the hinder end of the stomach and running forward 

 dorsal to the oesophagus is a large contractile heart. It propels the 

 blood forward to the branchiae, dividing in a right and left afferent 

 branchial vessel at the hinder border of the supra- oesophageal ganglion. 

 Each branch runs downwards to the inner side of the bi-anchias and 

 sends an afferent vessel into each gill-filament. This afferent vessel is 

 directly continuous with an efferent vessel at the tip of the filament, thus 

 forming a single vascular loop in each. The efferent vessels all open 

 into a single large efferent trunk running parallel to and outside the 

 afferent trunk. The efferent trunks unite in the mid-ventral line some 

 distance behind the mouth, to form the sub-intestinal vessel. The heart 

 id to be regarded as agastric blood- lacuna, which has become independent 



