224 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



5. A small sinus (sin. 5) receiving from the right anterior 

 portion of the ventral abdominal sinus. 



The union of the sinuses forms the large branchial sinus 

 or afferent branchial vessel (off. 6r.), which Hes immediately 

 beneath the floor of the pallial cavity posterior to the ctenidium. 

 The sinus enters the ctenidium on its outer concave side and 

 extends the whole length of this surface. On slitting up this 

 portion of the sinus, large gaping orifices are seen through 

 which the blood passes to the lamellae of the gill. There is 

 here, as in the tissues generally, no capillary system. 



From the ctenidium the blood is collected by two efferent 

 branchial vessels which lie along the inner, convex portion 

 of the gill (eff. br.). Like the afferent vessel the efferent vessels 

 communicate with the lamellae by wide openings. The 

 efferent vessels discharge into the auricle of the heart. 



All the blood from the ventral abdominal sinus does not 

 enter the ctenidium for purposes of aeration. At the level of 

 the heart there enters the kidney on its dorso-lateral face 

 a short sinus bringing blood from the left portion of the 

 haemocoele. (Fig. 15, ren. sin.) A small quantity of blood 

 from the left body wall and the anterior part of the left 

 parapodium also enters the renal sinus, and on the right side 

 of the kidney several small sinuses from the mantle and 

 pericardial roof open. (Fig. 15, ren. mant. sin. and ren. peri. 

 sin.) The renal sinus discharges into the lamellae of the 

 kidney, from whence the blood is collected by an efferent 

 vessel (Fig. 14, eff. ren.) and taken to the heart. There is 

 thus a renal portal system in Aplysia. The blood is collected 

 on the ventral side of the kidney, and, purified now from 

 nitrogenous waste matters, leaves by a short efferent renal 

 vessel situated on the right side of the kidney. The efferent 

 vessel opens into the base of the efferent branchial vessel, just 

 as the latter is about to open into the auricle. 



