186 ANNULATA. 
The blood-system is complex. ‘The blood is respiratory 
in function and is said to contain hemoglobin, giving it a 
red 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 rated blood from the Jast 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 #o 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 fosterior lateral vessels and two sudbintes- 
tinals 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 wsophageals on the cesophagus, 
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— 
Blood Vas- 
cular. 
Anterior Posterior 
Dorsal 
f, 7 Gills 
: Post” 
Ant ater 28!" lat im a: 
{ oe rer rnlesr ; 
Gills 
Ventral 
