PULSATION OF BLOOD VESSELS IN OYSTERS, OSTREA LURIDA AND O. GIGAS

¹ U. S. BUREAU OF FISHERIES

1. In the mantle of Ostrea lurida is a series of slowly pulsating blood vessels.

2. The many radial vessels are associated with the bundles of retractor muscle fibres of the mantle. The "accessory hearts" appear to be similar to these, though much larger.

3. The waste canal, a band of tissue running anteroposteriorly in the ventral wall of each mantle lobe and covered with cilia beating posteriorly, overlies a pulsating vessel which crosses and is continuous with many radial vessels.

4. All of the pulsating vessels communicate distally with the circumpallial sinus, which appears in this species not to be directly connected with the heart.

5. The vessels described pulsate at a slow rate and their activity is loosely coördinated.

6. The wave of contraction of the radial vessels originates centrally and travels slowly distally, forcing the blood outward into the circumpallial sinus. The pulsation of the vessel underlying the waste canal appears to begin at the anterior end.

7. The absence of effective valves is shown by the reversal of direction of flow of the blood as relaxation takes place.

8. The blood supply of the radial vessels appears to come from the blood spaces of the excretory organs and nearby tissues.

9. Isolated portions of the mantle of O. gigas, including an accessory heart, live for weeks, the accessory heart pulsating at approximately its normal rate. The rate of transmission of the impulse of contraction is slow, 4 to 8 mm. per second. The activity is compared to that of vertebrate smooth muscle.

10. The pulsating vessels appear to be indefinite spaces within the sub-epithelial matrix of connective tissue and smooth muscle, and an endothelium and other well-defined structures characteristic of formed blood vessels may be lacking.