c, p. a. 



vessels 



Figure 235. — Diagram of the circulation of blood in C. virginica. The position of various sinuses marked with capital 

 letters is indicated by broken lines; only one demibranch and one accessory heart are shown. A — auricles; A.cH. — 

 accessory heart of one side; P.S. — pallial sinuses; R.S. — renal sinuses; V — ventricle; V.S. — visceral sinuses; br.ef.v. — 

 branchial efferent vein; c.af.v. — common afferent vein; c.ef.v. — common efferent vein; ce.a. — cephalic artery; cp.a. — 

 circuinpallial artery; c.v. — cephalic veins; ga.a. — gastric artery; g.v. — gastric vein; h.a. — hepatic artery; h.v. — 

 hepatic vein; l.a. — labial artery; l.af.v. — lateral afferent vein; l.v. — labial vein; m.a. — adductor muscle artery; m.v. — 

 adductor muscle vein; p. a. — pallial arteries; p.af.v. — pallial afferent vein; p.ef.v. — pallial efferent vein; py.a. — pyloric 

 artery; r.a. — renal artery; r.g.a. — reno-geonadial artery; r.g.v. — reno-gonadial vein; r.v. — renal vein; tr.v. — tran.s- 

 verse veins of the gills. 



In visualizing the circulation of blood within 

 the gills one must keep in mind the location of the 

 five horizontal vessels at the top of the duplicated 

 W-shaped junctions of the gill lamellae (fig. 73). 



The course of circulation presented schemati- 

 cally in fig. 235 shows that the arterial blood goes 

 to the sinuses (P.S., V.S., R.S.) and then is con- 

 veyed through the afferent veins to the gills and 

 reaches the auricles via two common efTerent 

 veins. Some of the blood from the pallial sinuses 

 (P.S.) and from tlic renal sinus (R.S.) bypasses 

 the gills and is directly delivered to the auricles 

 through the common efferent veins. 



The deficiency in circulation caused by the 

 presence of large smuses is counteracted by the 

 pulsations of radial vessels of the mantle and by 

 a pau- of accessory hearts (Ac.H.), which function 

 independently of the principal heart of the oyster. 



The red and blue colors of the diagram show that 

 only oxygenated blood fills the heart. 



THE ACCESSORY HEART 



The accessory heart is a paired tubular struc- 

 ture along the inner surfaces of the right and left 

 mantle folds where they join together to form the 

 cloacal chamber. Its position on the wall of the 

 cloaca and its relation to the adjacent organs are 

 shown in figure 236 drawn from life. 



The accessory heart of the oyster is not the 

 simple tubular structure described by Hopkins 

 (1934, 1936) and Elsey (1935). It consists of 

 three branches of almost equal size, joined to- 

 gether at a common center (fig. 237). The entire 

 structure has the shape of the letter Y. The 

 lower or ventral branch (v.br.) extends along the 



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FISH AND WILDLIFE SERVICE 



