

BY WILLIAM A. HAKWELL, SI. A., B.SC. 651 



PSEUDOHZEMAL SYSTEM. 



The vascular systemofthe Serpulea has been treated of by several 

 anatomists — among the number Williams (1), Milne-Edwards 

 (2), Grube (3), Quatrefages (4), and Clarparede (5.) The most 

 detailed account of the coarse of the circulation is given by the 

 last-named author, who studied it chiefly in Spirographis Spal- 

 lanzanii, but ascertained that the same general arrangement holds 

 good in the Serpulidce. The leading peculiarity of the pseudo- 

 heernal system of this family, as of the Sabellidae, the Ammo- 

 charidse, the Ariciidae and the Cha^topteridse, consists in the 

 presence of a peri-intestinal vessel or sinus excavated in the 

 muscular wall of the alimentary canal, and extending from the 

 hinder extremity of the body as far as forwards as the oesophagus 

 and stomach. This peri-intestinal sinus takes the place of the 

 dorsal vessel found in other Annelids. It terminates in front, 

 according to Claparede, by breaking up into a network of small 

 vessels, which again further forward are gathered up into several 

 larger trunks, the two most important of these being the branchial 

 vessels. Throughout the greater length of the body the peri- 

 intestinal sinus is accompanied on the ventral side by a ventral 

 vessel. This gives off a pair of branches in each segment, and 

 ends in the thoracic region by breaking up into smaller vessels, 

 which join the capillary plexus. 



" Le mode de circulation chez les Sabelliens devient compre- 

 hensible par la description qui precede. Les ondes de contrac- 

 tion du sinus intestinal chassent le sang d'arriere en avant, comme 

 il est facile de s'en assurer sur le vivant. Ce sang remplit le 

 plexus cesophagien, et les deux vaisseaux branchiaux ont des 

 parois contractiles grace a un developpement musculaire rem ar- 

 guable. Une onde de contraction, parcourant d'arriere en avant 

 les vaisseaux branchiaux, chasse le sang jusqu'aux dernieres 



(1) British Association Report, 1851, p. 1ST- 



(2) " Recherches pour servir a 1' histoire de la circulation du sang chez les 

 Annelides " Ann. Sci. Nat. 2me. sir. X., p. 193. 



(3) " Anatomie der Kiemenwiirmer." 



(4) "Histoire Naturelle des Ainu-les marins et d'eau douce." 



(5) " Recherches sur la structure des Annelides siklentaires." 



