STEEBLOSPIO SHRUBSOLII. 



231 



shorter and more irregular from the lamellae. A similar outline characterises the anterior 

 "abdominal " region, but it is more rounded posteriorly (Fig. 124a). The first bristled 

 segment, already described, has shorter bristles than the succeeding, which, to the 

 number of seven, have capillary bristles both dorsally and ventrally. Bach has behind 

 it the membranous lamella. The winged hooks (Plate CIV, fig. 10) commence in 

 the ventral division at the eighth segment, a few capillary bristles accompanying them, 

 and they continue to the posterior end, the accompanying bristles becoming fewer. On 

 the dorsum of the second segment is a peculiar "dorsal collar" resembling a modified 

 dorsal lamella. 



The body- wall consists of cuticle, hypoderm, mucous glands, circular muscular fibres, 

 two dorsal and two ventral longitudinal muscles, the inner surface being lined with 

 coelomic epithelium. 







Fig. 124a.— Half section of the body-wall of Str 



\o through the posterior abdominal region, 



after Miss Florence Buchanan, mes. Dorsal mesentery ; c.ep. coelomic epithelium 



The alimentary canal presents a short protrusible and ciliated pharynx, behind which 

 is a narrow oesophagus, a wider region, and then the moniliform intestine which ends in 

 the anus. The terminal region of the gut is ciliated and may be respiratory. The wall 

 of the canal has from without inward coelomic epithelium, circular muscular fibres, and 

 cylindrical epithelium. Gregarines (Monocystis) are common in the intestine. 



The vascular system consists of a dorsal trunk, which gives off at the posterior 

 border of the prostomium a branchial vessel on each side, the returning trunk passing to 

 the ventral region to meet its fellow of the opposite side to form the ventral vessel. 

 Before they meet each is joined by the single trunk from the tentacle. The ventral 

 vessel reaches the posterior end and enters the sinus surrounding the intestine. Miss 

 Buchanan thought that a ridge on the dorsal wall of the intestine surrounded by the sinus 

 represented, perhaps, the heart-body in other Polychaeta, but this is uncertain. The 

 blood goes from behind forward in the dorsal vessel and in the sinus, which extends 

 from the posterior region to the anterior third ; from before backward in the ventral 

 vessel. Dorso-ventral vessels in the anterior region of the body connect the main trunks. 

 Two kinds of segmental organs (nephridia) occur. The first are two green tubes forming 



