38 BLOOMER : ANATOMY OF CERATISOLEN AND SOLECURTUS. 



just anterior to where the intestine lecaves it. The small bile duct opens 

 into the central division. 



The whole of the viscera in the proximal part of the foot is bound 

 together also with the pedal muscles, by a large quantity of connective 

 tissue. 



Circulatory System. 



Menegaux '^' states that the general circulatory system agrees with 

 that of Solen. 



The venous blood is collected into "the various sinuses, and from the 

 sinus of the viscero-parietal ganglion it is conveyed by the afferent branchial 

 vessels to the gills, and from them by the efferent branchial vessels to the 

 auricles. 



Over the posterior portion of the foot lies the large ventricle, with 

 large triangular auricles. The anterior aorta proceeds a short distance 

 along the rectum, until it reaches the muscular portion of the foot ; then 

 continues under the dorsal integument, and gives off a number of branches 

 which vascularise the viscera, anterior adductor muscle, the mantle lobes, 

 and the foot. The posterior aorta shortly after leaving the ventricle, forms 

 the dilation known as the bulbus arteriosus ; and then, dividing, continues 

 along the mantle lobes, and sends branches to the posterior adductor 

 muscle and the siphon. 



The gills extend horizontally from a position between the labial palps, 

 and level with the retractor pedis anterior muscles, right to the posterior 

 end of the proximal portion of the siphon. The inner parts of the bases 

 of the gills are connected together, while the outer parts are joined with 

 the walls of the siphonal chamber, thus separating the exhalent from the 

 inhalent chamber. When the siphon is contracted, the gills are folded 

 on themselves in a close mass, while in an extended condition these folds 

 disappear. 



The gills belong to the type whicli Dr. Ridewood '^' has termed 

 synaptorhabdic, and he states: "The lamellae are highly plicate, the 

 plicae being flattened anterio-posteriorly, so as to resemble the leaves of 

 a book. The number of filaments in a plica are about 30 in the outer, 



and 40 in the inner demi branch The principal filaments are 



large, and have a broad, shallow, frontal groove, from the middle of 

 which there sometimes arises .... a ridge of tall epithelial cells. 

 There is a fair amount of muscle fibre, running some vertically and 

 some liorizontally in relation with the principal filaments." 



The kidneys are situated posterior to the liver and elevator pedis 

 muscles, but do not extend far posteriorly ; while laterally they go a con- 

 siderable distance, passing along the mantle lobes to the siphonal retractor 

 muscles. Menegaiix '^' states the viscero-renal orifices exist as in Solen. 



" Recherches sur la circulation des Lamellibranches Mariiis, 1S'.)U. 

 i Phil. Trans, iy03 (ser. B.), vol. 195, pp. 147-:iS4. 

 6 Up. vil. 



