Miscellaneous. 157 



MISCELLANEOUS. 



On some Points in the Anatomy of the Common Alxissel (Mytilus edulis). 

 By M, A. S.ujAxiER. 



In tho mussel the apparatuses of circulation, respiration, and 

 urinary excretion present uiTanp^emcnts which differ in some respects 

 from those observed in tho Lamellibranchiate Mollusca generally. 



The central apparatus of circulation consists of a heart with two 

 auricles, which does not furnish an aorta at its posterior extremity. 

 This aorta springs from the anterior aorta at the lower surface of 

 the aortic bulb, and passes backward to supply the stomach and in- 

 testine. The anterior aorta furnishes the hepatic and tentacular 

 arteries and especially the great parallel arteries which are distributed 

 over the outer surface of the mantle. 



The return passages of tho blood to the heart are very complex, 

 and vary according to tho organs. On each side of the body there 

 is a great vessel, running obliquely from above downwards and from 

 the front backwards, which opens directly into the auricle ; this is 

 the oblique afferent vein. Its lower extremity opens into a large 

 longitudinal cavity, situated at the level of the adherent margin of 

 the mantle and composed of two parts, a posterior and an anterior 

 longitudinal vein. 



The veins of the mantle are placed on the inner surface. They 

 ascend towards the adherent margin of the mantle, and anastomose 

 below this margin to form a large, zigzag, horizontal vein. From 

 the superior angles of this sinuous trunk spring vertical trunks, which 

 soon subdivide into small canals to penetrate into some special organs, 

 which 1 shall describe under the name of plaited or frilled organs. 

 The blood which has traversed these organs penetrates in part into 

 the vascular network of the corjnis Bojani, and in part into the 

 anterior longitudinal vein. The blood coming from the liver and 

 the anterior visceral mass penetrates directly into the corpus Bojani. 

 A small portion of the blood from the mantle passes, also directly, 

 into the oblique afferent vein, and another portion directly into the 

 anterior longitudinal vein. 



The coipus Bojani is far from presenting the characters seen in it 

 in most Lamellibranchiate Mollusca. It does not form a clearly 

 distinct organ as in these Mollusca ; but neither is it entirely com- 

 posed, as has been asserted, of plates of Bojanian tissue lining the 

 walls of the large veins and auricles. In fact we can distinguish 

 in the corpus Bojani of the mussel two different parts — one autono- 

 mous, the other dependent on the large veins. The autonomous 

 part is anterior, and is to be seen on the lateral portions of tho 

 liver, in tho furrow which soparates that organ from the base of the 

 branchiae ; it is formed of a series of vertical membranous folds, and 

 is of a greenish brown colour. The folds enclose cavities which 

 open successively by their superior extremities into a collecting 

 canal, the diameter of which increases rapidly from before back- 

 wards, and which is exactly within the afferent vessel of tho branchia. 



