ACCESSORY HEARTS IN THE OYSTER, OSTREA GIGAS

¹ U. S. BUREAU OF FISHERIES

In three species of Ostrea a pair of actively pulsating accessory hearts was observed in the lateral walls of the cloacal chamber. They appear to pump blood from the lacunae of the excretory organs into the large marginal arteries of the mantle lobes and into the gills.

Counts of the rate of pulsation of heart and accessory hearts in O. gigas show that they act independently, the rate of pulsation of the accessories probably being determined by the rate at which they fill with blood. Only in this respect is their rate dependent upon the heart rate.

The accessory hearts appear to be homologous to the gill hearts of cephalopods.

The course of circulation, as influenced by the accessory hearts, is apparently as follows: blood from the ventricle passes through large arteries to the viscera, adductor muscle, and palps; the anterior aorta is directly continuous with the marginal arteries of the mantle; venous blood from viscera, palps, gills, and muscle passes to the excretory organs from which it is pumped by the accessory hearts into the marginal arteries of the mantle and to the gills; blood collected from the mantle returns directly to the auricles.

Heart and accessories both pump blood into the marginal arteries, which therefore receive both venous and arterial, purified and unpurified blood.