ANATOMY OF THE LAMELLIBRANCHIATA. 107 



CIRCULATING SYSTEM. 



This system is not so simple as it is described by Cuvier, 

 Poli, &c. Bojanus 1 in the Anadonta first described its cor- 

 rect anatomy. By means of mercurial injections it may bt 

 readily made out in the common scallop or Pecten maximus 

 The venous blood from the liver, ovaries and intestine, does 

 not go to the branchice immediately, but a portion of it en- 

 ters, on each side, a sinus or system of veins situated upon 

 the adductor muscle, the remainder is poured into a large 

 vessel, which is distributed to a dark coloured excretory or- 

 gan, situated at the base of the branchice on each side. 

 These organs have other veins which open either into 

 the sinus or into the branchial arteries. The sinus receives 

 likewise the veins of the muscle, and also in part the blood 

 of the mantle. It opens into the branchial arteries by two 

 valvular openings. The blood from the viscera must in great 

 part pass through the tissue of the excretory organs to enter 

 the branchial artery, and the tissue itself appears to be 

 entirely formed by these veins. Bojanus from this considers 

 these bodies as the organs of respiration. The auricles, 

 besides the branchial veins, receive the extremities of the 

 large veins of the mantle, small hepatic branches, and 

 other veins from the neighbouring parts. Poli has figured 

 this circumstance in the Area, Spondylus, fyc. The branchial 

 artery then has its principal origin from the large veins or 

 venous sinus, situated upon the adductor muscle; it then 

 receives veins from the organs above mentioned, also others 

 from the root of the branchiae and from the mantle : it 

 then at regular distances gives branches to the processes 

 of the branchice, which run into the corresponding ramuscu- 

 les of the branchial vein. The branchial vein, formed 

 by these ramuscules, lies nearer to the processes of the two 

 vessels, and is crossed by the divisions of the artery ; it is 

 joined by the extremity of the great vein of the mantle, and 

 by small veins from the liver, &c, as described above, and 

 forms the auricle. No valve exists between the veins and 

 auricles. The latter have projecting processes upon them, 

 secreting perhaps the fluid of the pericardium. They are 

 connected by a transverse vein, receiving some small ves- 

 sels from the pericardium, &c. A valve formed by two 

 semilunar membranes exists at the entry of each auricle into 

 the ventricle. The pericardium, always situated in the 



1 A translation of his paper may be found, ' Journ. de Physique,' t. 89, 

 witli observations upon it by M. Blainville. 



