h, Hinge; l, ligament; d, pg, and sg, connective, and two ganglia of the nervous system; p, palps; br, blood-vessel from gills to auricle of heart; au, auricle; ve, ventricle; s, external opening of sexual and renal organs of right side; bp, pores from which the water issues into the branchial canals after passing through the gills: mt, mantle (the arrows showing the direction of currents produced by cilia); g, gills; gc, cavity between the two mantle folds; cl, cloaca; am, adductor muscle (cut across); bj, outline of organ of Bojanus, the so-called ‘kidney.’