522. TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
leading into small caeca. Hence the wall of the branchial 
heart is penetrated in every direction by a system of short 
vessels, which lead ultimately into the lumen of the 
heart. Therefore venous blood, on entering the organ, 
penetrates into this system of vessels before it passes on 
into the afferent vessel which is given off at the antero- 
external angle of the heart. Cuénot considers that the 
purplish colour of the branchial heart is due to the 
purplish concretions found in the cells of which it is 
composed. By experiment he has proved that these cells 
are excretory, and therefore that the branchial heart is a 
glandular organ. The venae cavae, branchial hearts and 
vessels, and main aortae, as well as the heart, are all 
rhythmically contractile. 
The Venous Sinus extends from behind the mouth to 
the posterior edge of the stomach, and is divided into three 
cavities 
anterior, central and posterior, the first two of 
which communicate by important vessels with the large 
veins. The wall of the sinus is a tough transparent 
membrane. 
1. ‘The anterior division is small and is joined to the 
middle division by a narrow region, which runs with the 
oesophagus through the cavity of the ring-like central 
nervous system (fig. 53). The thin wall becomes adherent 
to the buccal mass about half-way down its length 
(fig. 53, B.M.), thus forming the anterior boundary of 
the sinus. Hence the posterior portion of the buccal 
mass, the anterior salivary glands, and the anterior 
portion of the oesophagus, are bathed in the blood 
contained in this division of the venous sinus. 
2. The central division is much larger, and 
narrower in the middle region than at its two extremities, 
and contains the oesophagus, crop, posterior salivary 
glands and stomach, However, the liver and ink sae, 
