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THE ANATOMY OF THE BRITISH SPECIES OF 

 THE GENUS SOLEN. rt. ii.* 



By II. H. BLOOMER. 

 (Plate viii.) 



Circulatory System. 



The circulatory system of Solen presents not a few difficulties. In 

 the following account I have been guided very largely by the valuable 

 work of Menegaux, but the whole system has been subjected to very 

 careful investigation, particularly the venous system. 



Venous Sijdem. — Solen ends, L. (PI. viii, fig. 17). 



As in all the Pelecypoda, the venous system of Solen is very com- 

 plicated and difficult to make out. There are no defined vessels 

 conveying the venous blood from the tissues, but it finds its way 

 through the lacunous parts of the animal and accumulates in the 

 various sinuses. 



Running along the elongated foot is a large canal, the homologue 

 of the posterior pedal sinus of other pelecypoda (P.S.). It is nearly 

 median and enclosed by the bundles of longitudinal and transverse 

 muscles, leaving between them, openings by which the blood 

 passes to it from the secondary sinus, the latter being situated dorsally 

 (A.P.S.). 



The posterior pedal sinus branches at the proximal end of the 

 foot into anterior and posterior divisions, the latter following inferiorly 

 the visceral mass, from which it receives the blood, and describing a 

 curve terminates just opposite the viscero-renal orifices {V.R.O.). In 

 the retraction of the foot the orifices open and allow the blood 

 to pass through the kidneys (A'.). The blood then accumulates 

 in the pallial sinuses (Fa. S.), which are situated on the inner 

 surfaces of the mantle lobes near to tlie line of their dorsal concres- 

 cence, and just behind the posterior adductor muscle (P. A.). The 



* See ante, p. 36. 



