The heart c lying in the pericardium is seen in close proximity to the renal organ, and consists of a single auricle receiving blood from the gill, and of a single ventricle which pumps it through the body by an anterior and posterior aorta.
Whether the pericardium and the ventral sinus are made to expand simultaneously or all the movement is made by one only of the surfaces concerned, must depend on conditions of tension.
The heart lying within the adjacent pericardium has the usual form, a single auricle and ventricle.
When the pericardium is cut open from above in an animal otherwise entire, the anterior face of the kidney is seen forming the posterior wall of the pericardial chamber; on the deep edge of this face, a little to the left of the attachment of the auricle to the floor of the pericardium, is seen a depression; this depression contains the opening from the pericardium into the kidney.
Internally this glandular sac presents a second slit or aperture which leads into the pericardium (as is now found to be the case in all Mollusca).
Floor of the pericardium separating that space from the non-glandular portion of the nephridia.
The existence of two renal organs in Patella, and their relation to the pericardium (a portion of the coelom), is important.
The gonad is transversely wrinkled and lies between the aorta and the intestine, extending from the pericardium to the anterior end of the body.
The blood, which is a non-corpuscular fluid, is propelled forwards by the contractile dorsal vessel and collected into the central bloodsinus; this lies over the stomochord, and is surrounded on three sides by a closed vesicle, with contractile walls, called the pericardium (Herzblase).
A, Pericardium opened dorsally a, Ventricle of the heart.