NATURAL HISTORY OF THE BAY SCALLOP 
591 
CIRCULATORY SYSTEM 
The circulatory system of the giant sea scallop, Peden tenuicostatus or Peden 
grandis (seep. 571) has been studied by Drew (1906) and that of P. maximus by Dakin 
(1909), with such close agreement as to path followed, except for the quite different 
gills, that it may be assumed that the circulation of P. irradians is very much like 
that of these forms. This assumption receives support from such observations as 
are readily made, as of the vascular network of the mantle and of the veins of the 
visceral mass. Circulation, therefore, may be summarized as follows: Blood leaves 
the ventricle by the anterior and posterior aortse. The posterior aorta supplies the 
adductor muscle, the rectum, and, through the large posterior pallial artery and the 
circumpallial artery, the mantle. The anterior aorta supplies the remainder of the 
body and, through the anterior pallial artery, contributes blood to the circumpallial 
artery. Blood from the mantle, after passing through a net work, returns directly 
Figure 12. — Main vascular circulation, except for mantle and gills (after Dakin) : a, Arterial circulation; b, 
venous luriccation; A. P. A., anterior pallial artery. A. P. P., posterior pallial artery; A. Add., adductor; 
Ao. A, anterior aorta; Ao. P, posterior aorta; A. P., pedal artery; Aur., right auricle; A. V., visceral arteries; 
F, foot; K., kidney; Lp., lips; S. D., dorsal venous sinus; St., tissue surrounding the stomach; S. V., ventral 
venous sinus; V. V., viscereal veins 
to the heart. According to Dakin the venous system consists largely of sinuses (see 
fig. 12b), contrasting with the definite vessels of the arterial system. Large sinuses 
between the adductor and its sheath and paired veins from the visceral mass and 
digestive diverticula convey venus blood to the kidneys, which receive all the blood 
except that of the mantle. From the kidneys the blood passes to the gills and thence 
to the heart. Figure 12, after Dakin, shows the main arterial and venous circulation 
except for the mantle and gills. 
The symmeti'ical heart consists of two auricles and one ventricle. The auricles 
are relatively large and very uneven of surface. The ventricle, traversed by the 
rectum, is greatly reduced in size when contracted and is smooth exteriorly. Drew 
described muscles around the openings of the auricles which he believed acted as 
sphincters to prevent the back flow of blood from the ventricle. The firm walled, 
triangular pericardium lies in the angle formed by the posterio-ventral surface of 
stomach and digestive diverticula, on the one hand, and the dorsal surface of the 
adductor muscle on the other. It extends from one pallial lobe to the other. 
10441 — 31—4 
