The blood of the snail consists of a colorless plasma containing corpuscles and serves to transport nutriment, oxygen, and waste products from one part of the body to another. The heart lies in the pericardial cavity. The muscular ventricle forces the blood through the blood vessels by rhythmical pulsations. One large aorta arises at the apex of the ventricle; this give rise at once to a posterior branch, which supplies chievly the digestive gland, stomach, and ovotestis, and an anterior branch, which carries blood to the head and foot. the blood passes from the arterial capillaries into venous capillaries and flows through these into sinuses. Viens lead from these sinuses to the wall of the mantle cavity, where the blood, after taking in oxygen and giving off carbon dioxide, enters the pulmonary vein and is carried to the single auricle and finally into the ventricle again.