SEA-FISHERIES LABORATORY. DAT 
The second focus of the venous blood is the renal sinus, 
towards which all the blood circulating in the viscero- 
pedal mass converges. There are two large sinuses in 
the latter, an irregular sinus lying on the anterior margin 
and a posterior pedal sinus (Szn.p.) lying beneath the 
internal part of the posterior retractor muscles of the foot. 
As the latter are gathered up into the two compact muscle 
bundles which run upwards through the renal organ, they 
leave an opening in the muscular wall of the foot which 
leads into the two short longitudinal trunks, these, finally, 
open into the large central sinus in the middle of the renal 
organ (Sz.ren., figs. 7 and 30). 
From this central space the venous blood flows outwards, 
bathing the renal secretory tubules in its course, and 
enters two longitudinal vessels which run along the bases 
of the ctenidia. These are the common afferent branchial 
vessels (Br.aff., fig. 30). From them a series of vessels, 
running perpendicularly to the bases of the ctenidia, enters 
each branchia—the afferent branchial vessels (Br.aff’., figs. 
26 and 30). These communicate through the interfila- 
mentar branchial junctions with a series of similarly 
disposed vessels—the efferent branchial vessels (Br.eff"., 
figs. 26 and 30), which fall into a pair of common efferent 
branchial vessels (Br.eff.), and these finally open into the 
auricles. From the auricles the blood enters the ventricle 
through the openings at the apices of the former, reflux 
being prevented by the action of the valves guarding these 
openings. 
Menégaux* bases a theory accounting for the protrusion 
of the foot, siphons, and mantle edges, on the anatomical 
relationships indicated above, 7.e., the presence of a valve 
* Recherches Sur le Circulation des Lamellibranches Marins. 296 pp., 
Besancon, 1890. Also Comptes Rendus de |’Acad. Sci., Paris, T, CVIIL., 
pp. 361—364, 1889. 
