BY WILLIAM A. HASWELL, M.A., B.SC. 653 



qui s'y trouve ; penetrer dans 1' organe respiratoire, en sortir 

 et suivre une marche inverse d' avant en arriere par le tronc 

 infurieur." Here the "grand tronc superieur " must be the 

 peri-intestinal sinus, not the dorsal vessel, and the view of the 

 course of the blood is, on the whole, correct. 



In some of the species in which I have specially studied the 

 circulation, the arrangement is somewhat different from that 

 described by Claparede as obtaining in Spirographis, so that 

 there would seem to be considerable variation in this respect 

 even within the limits of a single family. 



In all the intestine is surrounded throughout the greater part 

 of its length by a peri-intestinal sinus which gives off numerous 

 branches to the segments. In Eupomatus elegans, this sinus ends 

 in front in the oesophageal region of the body and opens into a 

 short wide dorsal sinus or cardiac sac (pi. XXXI., fig. 2, d. s. 

 and fig. 3, h. t.) ; passing off from this in front are a pair of 

 trunks (fig. 2, d. b. v.) which run forwards and outwards 

 for a short distance to the base of the branchiae where each 

 unites with a similar branch from the ventral vessel to form 

 the common branchial vessel (c, b. v.) of the right or the left 

 side as the case may be. The latter runs in an arched 

 manner along the bases of the branchiae giving off a single 

 branch to each of them, and one to the operculum and the pseud- 

 operculum. The ventral vessel (fig. 1, a ; fig. 2, v. v.) is a distinct 

 wide trunk which is continued along the whole length of the body 

 beneath the p6ri-intestinal sinus ; in front it bifurcates, each 

 of the branches presenting a contractile dilatation (fig. 2, v. v'.) 

 at its base, and in front communicating with the branches 

 from the dorsal sinus to form the common branchial vessels as 

 above described. The rich network of capillaries in the collarette 

 and lateral flaps receives its blood from the ventral vessel, and 

 the circulation is here, as in the branchiae, a to-and-fro one, 

 the same vessels acting both as afferent and efferent trunks fur 

 the capillary networks. 



The course of the blood in Eupomatus is as follows: — 



The blood which enters the peri-iatestinal sinus by the 

 segmental vessels is carried forward by peristaltic contractions to 

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