i86 ANNULATA. 



The blood-system is complex. The blood is respiratory 

 in function and is said to contain haemoglobin, giving it a 

 Blood Vas- ^^^ colour. The vessels lie between the coelomic 

 epithelium and the alimentary canal or the body- 

 wall, as the case may be. Along the whole 

 length of the alimentary canal runs a median dorsal 

 vessel in which the blood runs forwards. It supplies 

 branches to the alimentary canal throughout its course, 

 and it receives aerated blood from the last seven pairs 

 of gills by paired efferent branchials. Below the ali- 

 mentary canal, but hanging free from it, runs the median 

 ventral vessel. Its chief branches are thirteen pairs of 

 afferent branchials taking blood to the gills and some to the 

 nephridia. In this vessel the blood flows backwards, and 

 it drains the regions of the alimentary canal supplied by 

 the dorsal vessel. At the commencement of the stomach 

 there are a pair of hearts. Each is two-chambered, consist- 

 ing of an auricle and a ventricle. On contraction of the 

 ventricles on each side the blood from the heart is driven 

 into the ventral vessel. 



Over the stomach is a plexus of vessels, of which we may 

 discern the two posterior lateral vessels and two siihintes- 

 tiiials in the ventral wall of the stomach. 



The subintestinals receive blood from the first six pairs 

 of gills by six efferent branchials on each side. The 

 subintestinals communicate through small vessels with 

 the posterior laterals, which carry the blood forwards 

 and, together with paired oesophageals on the oesophagus, 

 fall on each side into the auricle of the heart. On con- 

 traction of the heart the blood is driven through the 

 ventricles and thence into the ventral vessel. We may 

 summarise this rather complex arrangement by a diagram — 



AnTenor Posterior 



Dorsdl 



-^ 



7G.II5 



Y ■ ^''^v\ , ^ Sub. '"f"^ 



J^ 



Venfrdl 



