LAMELLIBRANCHIATA 581 



The visceral vessels likewise return blood to the kidney network 

 so that practically the whole of the blood passes through the excretory 

 organ and is purified. A part of the blood from the kidney network 

 enters the ctcjiidial circulation, discharging into the longitudinal 

 afferent branchial vein, which gives off to each filament a vessel which 

 descends one side and ascends the other. The ascending vessels join 

 to form a longitudinal efferent vessel, which discharges into the longi- 



Viscera 



Ipdney 



eff.c.v.- 



.aff.c.v. 



Ctenidia 



Fig. 397. Circulation of Anodonta. A, Simplified diagram to show the course 

 of the blood, indicating the relative importance of the various branches. 

 Vessels returning arterial blood to the heart shown in black. B, Transverse 

 section of Anodonta to show part of the course of the circulation. In the foot, 

 F., the veins run into the vena cava cut in section, from which a small part 

 of the blood is returned direct to the auricle in the dorsal wall of the bladder, 

 bl., the rest through the kidney, k., longitudinal afferent vessels, Iv/, and 

 thence to the afferent system of vessels in the ctenidium, ajf.c.v. On the other 

 side the efferent system of vessels, eff.c.v., is shown returning blood to the 

 longitudinal vessels at the base of the ctenidia, v.'\ from which it passes to the 

 auricle, au., through an irregular system of blood spaces. The pallial circula- 

 tion is not shown here. sbr. epibranchial space; v.c. vena cava; ven. ventricle. 



tudinal vein of the kidney. Into this longitudinal vein is collected the 

 blood from the kidney network in general and by this channel blood 

 is returned into the auricle. It will be seen that the branchial cir- 

 culation is not important in Mytilus ; in Anodonta (Fig. 397) it is more 

 developed. 



In Anodonta (Fig. 397) where the foot is larger than in Mytihis 

 and movement more continuous the pedal artery is more impor- 



