One can imagine the interest and astonishment with which the great Greek would have been filled had some unduly precocious disciple shown to him the red-blood-system of the marine terrestrial Annelids; the red blood of Planorbis, of Apus cancriformis, and of the Mediterranean razor shell, Solen legumen.
In Ceratisolen legumen, various species of Arca and a few other species the blood is crimson, owing to the presence of corpuscles impregnated with haemoglobin.
A good case for the examination of the question as to whether blood enters the pericardium of Lamellibranchs, or escapes from the foot, or by the renal organs when the animal suddenly contracts, is furnished by the Ceratisolen legumen, which has red blood-corpuscles.
According to observations made by Penrose on an uninjured Ceratisolen legumen, no red corpuscles are to be seen in the pericardial A space, although the heart is filled with them, and no such corpuscles are ever discharged by the animal when it is irritated.