ELEDONE. 511 
is asymmetrical in shape. The walls of this chamber are 
muscular and, unlike the dark coloured branchial hearts, 
of a whitish colour. The inner surface is produced into 
numerous branching and interlacing fleshy pillars, which 
are bathed in arterial blood (PI. VI, fig. 45). The cavity 
of the ventricle is incompletely divided into two chambers 
by a fleshy partition which probably aids in ensuring the 
distribution of blood through all three aortae during the 
period of systole. This is triangular in shape, and as 
the dorsal and anterior edges are attached to the 
corresponding walls of the heart, while the basal side 
hangs free, an incomplete vertical septum is thus formed. 
(Pl. VI, figs. 47 a and 3, ér. s., and fig. 40). The right 
auricle leads into the right chamber, and the left auricle 
similarly into the left chamber of the ventricle. The 
anterior aorta is given off from the right anterior dorsal 
corner of the heart, while the abdominal aorta leads out 
of the ventral surface of the left chamber and the genital 
aorta from the posterior dorsal wall of the same (figs. 
45, 46 and 47). Two semi-lunar valves guard the entrance 
of each auricle into the ventricle. The free edge of each 
is directed inwards into the ventricle (fig. 48, aw. v. and 
au,v,). Consequently, at the moment of diastole they 
open and allow blood to enter the ventricle from the 
auricles, and at this time the blood in the two chambers 
of the ventricle can mix freely. However, at the moment 
of systole the valves close and prevent the reflux of blood 
into the auricles. The ventricle is now completely 
divided into two chambers by the partition, and the 
blood from the right chamber is forced up the anterior 
aorta, while the blood in the left flows into the abdominal 
and genital aortae. ‘The anterior aorta also has two 
smaller semi-lunar valves at its base. These have their 
free edges turned towards the aorta. They close during 
diastole, and open during systole. 
